Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Dec. 31, 2017	Feb. 15, 2018	Jun. 30, 2017
Document and Entity Information
Entity Registrant Name	Transocean Ltd.
Entity Central Index Key	0001451505
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 3.2
Entity Common Stock, Shares Outstanding		458,914,707
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating revenues
Contract drilling revenues	$ 2,731	$ 3,705	$ 6,802
Other revenues	242	456	584
Total operating revenues	2,973	4,161	7,386
Costs and expenses
Operating and maintenance	1,388	1,875	2,955
Depreciation	832	893	963
General and administrative	156	172	192
Total costs and expenses	2,376	2,940	4,110
Loss on impairment	(1,498)	(93)	(1,875)
Gain (loss) on disposal of assets, net	(1,603)	4	(36)
Operating income (loss)	(2,504)	1,132	1,365
Other income (expense), net
Interest income	43	20	22
Interest expense, net of amounts capitalized	(491)	(409)	(432)
Gain (loss) on retirement of debt	(55)	148	23
Other, net	4	43	37
Total other income (expense), net	(499)	(198)	(350)
Income (loss) from continuing operations before income tax expense	(3,003)	934	1,015
Income tax expense	94	107	120
Income (loss) from continuing operations	(3,097)	827	895
Income (loss) from discontinued operations, net of tax			2
Net income (loss)	(3,097)	827	897
Net income attributable to noncontrolling interest	30	49	32
Net income (loss) attributable to controlling interest	$ (3,127)	$ 778	$ 865
Earnings (loss) per share-basic
Earnings (loss) from continuing operations (in dollars per share)	$ (8.00)	$ 2.08	$ 2.36
Earnings (loss) per share (in dollars per share)	(8.00)	2.08	2.36
Earnings (loss) per share-diluted
Earnings (loss) from continuing operations (in dollars per share)	(8.00)	2.08	2.36
Earnings (loss) per share (in dollars per share)	$ (8.00)	$ 2.08	$ 2.36
Weighted-average shares outstanding
Basic (in shares)	391	367	363
Diluted (in shares)	391	367	363

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)
Net income (loss)	$ (3,097)	$ 827	$ 897
Net income attributable to noncontrolling interest	30	49	32
Net income (loss) attributable to controlling interest	(3,127)	778	865
Components of net periodic benefit costs before reclassifications		(20)	63
Components of net periodic benefit costs reclassified to net income	21	8	23
Other comprehensive income (loss) before income taxes	21	(12)	86
Income taxes related to other comprehensive income	(28)	6	(17)
Other comprehensive income (loss)	(7)	(6)	69
Other comprehensive income (loss) attributable to controlling interest	(7)	(6)	69
Total comprehensive income (loss)	(3,104)	821	966
Total comprehensive income attributable to noncontrolling interest	30	49	32
Total comprehensive income (loss) attributable to controlling interest	$ (3,134)	$ 772	$ 934

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets
Cash and cash equivalents	$ 2,519	$ 3,052
Short-term investments	450
Accounts receivable, net
Trade	597	833
Other	44	65
Materials and supplies, net	418	561
Restricted cash accounts and investments	466	466
Other current assets	112	121
Total current assets	4,606	5,098
Property and equipment	22,693	27,372
Less accumulated depreciation	(5,291)	(6,279)
Property and equipment, net	17,402	21,093
Deferred income taxes, net	47	298
Other assets	355	400
Total assets	22,410	26,889
Liabilities and equity
Accounts payable	201	206
Accrued income taxes	79	95
Debt due within one year	250	724
Other current liabilities	839	960
Total current liabilities	1,369	1,985
Long-term debt	7,146	7,740
Deferred income taxes, net	44	178
Other long-term liabilities	1,082	1,153
Total long-term liabilities	8,272	9,071
Commitments and contingencies
Redeemable noncontrolling interest	58	28
Shares, CHF 0.10 par value, 417,060,033 authorized, 143,783,041 conditionally authorized and 394,801,990 issued at December 31, 2017 and 2016 and 391,237,308 and 389,366,241 outstanding at December 31, 2017 and 2016, respectively	37	36
Additional paid-in capital	11,031	10,993
Retained earnings	1,929	5,056
Accumulated other comprehensive loss	(290)	(283)
Total controlling interest shareholders' equity	12,707	15,802
Noncontrolling interest	4	3
Total equity	12,711	15,805
Total liabilities and equity	$ 22,410	$ 26,889

CONSOLIDATED BALANCE SHEETS (Parenthetical) $ in Millions	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares
Materials and supplies, allowance for obsolescence \| $	$ 141	$ 153
Shares, authorized	417,060,033	417,060,033
Shares, conditionally authorized	143,783,041	143,783,041
Shares, issued	394,801,990	394,801,990
Shares, outstanding	391,237,308	389,366,241
Maximum
Allowance for doubtful accounts \| $	$ 1	$ 1

CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) shares in Millions, $ in Millions	Total controlling interest shareholders' equity	Shares	Additional paid-in capital	Treasury shares, at cost	Retained earnings	Accumulated other comprehensive loss	Noncontrolling interest	Total
Balance at Dec. 31, 2014	$ 13,793	$ 5,169	$ 5,797	$ (240)	$ 3,413	$ (346)	$ 311	$ 14,104
Balance (in shares) at Dec. 31, 2014		362
Increase (Decrease) in Shareholders' Equity
Share-based compensation	64		64					64
Issuance of shares under share-based compensation plans		$ 24	(24)
Issuance of shares under share-based compensation plans (in shares)		2
Reclassification of obligation for distribution of qualifying additional paid-in capital	(109)		(109)					(109)
Allocated capital for transactions with holders of noncontrolling interest	9		9				(9)
Net income (loss) attributable to controlling interest					865			865
Other comprehensive income (loss) attributable to controlling interest						69		69
Total comprehensive income attributable to noncontrolling interest							38
Total comprehensive income (loss) attributable to controlling interest	934							934
Total comprehensive income (loss)								972
Acquisition of noncontrolling interest							(1)	(1)
Distributions to holders of noncontrolling interest							(29)	(29)
Other, net	(1)		(1)					(1)
Balance at Dec. 31, 2015	14,690	$ 5,193	5,736	(240)	4,278	(277)	310	15,000
Balance (in shares) at Dec. 31, 2015		364
Increase (Decrease) in Shareholders' Equity
Share-based compensation	42		42					42
Reduction of par value		$ (5,159)	5,159
Cancellation of shares held in treasury			(240)	$ 240
Issuance of shares for acquisition of noncontrolling interest, net of issue costs	315	$ 2	313					315
Issuance of shares for acquisition of noncontrolling interest (in shares)		24
Issuance of shares under share-based compensation plans (in shares)		1
Allocated capital for transactions with holders of noncontrolling interest	(18)		(18)				18
Net income (loss) attributable to controlling interest					778			778
Other comprehensive income (loss) attributable to controlling interest						(6)		(6)
Total comprehensive income attributable to noncontrolling interest							26
Total comprehensive income (loss) attributable to controlling interest	772							772
Total comprehensive income (loss)								798
Acquisition of noncontrolling interest							(321)	(321)
Distributions to holders of noncontrolling interest							(30)	(30)
Other, net	1		1					1
Balance at Dec. 31, 2016	15,802	$ 36	10,993		5,056	(283)	3	15,805
Balance (in shares) at Dec. 31, 2016		389
Increase (Decrease) in Shareholders' Equity
Share-based compensation	41		41					41
Issuance of shares under share-based compensation plans		$ 1	(1)
Issuance of shares under share-based compensation plans (in shares)		2
Net income (loss) attributable to controlling interest					(3,127)			(3,127)
Other comprehensive income (loss) attributable to controlling interest						(7)		(7)
Total comprehensive income attributable to noncontrolling interest							1
Total comprehensive income (loss) attributable to controlling interest	(3,134)							(3,134)
Total comprehensive income (loss)								(3,133)
Other, net	(2)		(2)					(2)
Balance at Dec. 31, 2017	$ 12,707	$ 37	$ 11,031		$ 1,929	$ (290)	$ 4	$ 12,711
Balance (in shares) at Dec. 31, 2017		391

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income (loss)	$ (3,097)	$ 827	$ 897
Adjustments to reconcile to net cash provided by operating activities:
Depreciation	832	893	963
Share-based compensation expense	41	42	64
Loss on impairment	1,498	93	1,875
(Gain) loss on disposal of assets, net	1,603	(4)	35
(Gain) loss on retirement of debt	55	(148)	(23)
Deferred income tax expense (benefit)	89	68	(134)
Other, net	55	14	74
Changes in deferred revenues, net	33	219	(90)
Changes in deferred costs, net	54	72	179
Changes in other operating assets and liabilities, net	(19)	(165)	(395)
Net cash provided by operating activities	1,144	1,911	3,445
Cash flows from investing activities
Capital expenditures	(497)	(1,344)	(2,001)
Proceeds from disposal of assets, net	350	30	54
Deposits into short-term investments	(450)
Other, net	10	1	15
Net cash used in investing activities	(587)	(1,313)	(1,932)
Cash flows from financing activities
Proceeds from issuance of debt, net of discounts and issue costs	1,144	2,401
Repayments of debt	(2,284)	(2,295)	(1,506)
Deposits to cash accounts restricted for financing activities	(97)	(85)
Proceeds from cash accounts and investments restricted for financing activities	150	124	110
Distributions of qualifying additional paid-in capital			(381)
Distribution to holders of noncontrolling interest		(30)	(29)
Other, net	(3)		(3)
Net cash provided by (used in) financing activities	(1,090)	115	(1,809)
Net increase (decrease) in cash and cash equivalents	(533)	713	(296)
Cash and cash equivalents at beginning of period	3,052	2,339	2,635
Cash and cash equivalents at end of period	$ 2,519	$ 3,052	$ 2,339

Business	12 Months Ended
Business	Dec. 31, 2017
Business
Business	Note 1—Business Overview—Transocean Ltd. (together with its subsidiaries and predecessors, unless the context requires otherwise, “Transocean,” “we,” “us” or “our”) is a leading international provider of offshore contract drilling services for oil and gas wells. We specialize in technically demanding sectors of the offshore drilling business with a particular focus on ultra‑deepwater and harsh environment drilling services. Our mobile offshore drilling fleet is considered one of the most versatile fleets in the world. We contract our drilling rigs, related equipment and work crews predominantly on a dayrate basis to drill oil and gas wells. At December 31, 2017, we owned or had partial ownership interests in and operated 39 mobile offshore drilling units, including 26 ultra‑deepwater floaters, seven harsh environment floaters, two deepwater floaters and four midwater floaters. At December 31, 2017, we also had three ultra‑deepwater drillships under construction or under contract to be constructed. See Note 5—Drilling Fleet. Business combination—On August 13, 2017, we entered into a transaction agreement (as amended, the “Transaction Agreement”) with Songa Offshore SE, a European public company limited by shares, or societas Europaea, existing under the laws of Cyprus (“Songa”), pursuant to which we agreed to offer to acquire all of the issued and outstanding shares of Songa, subject to certain conditions, through a public voluntary exchange offer (the “Offer”). At December 31, 2017, Songa owned and operated seven mobile offshore drilling units, including five harsh environment floaters and two midwater floaters. See Note 20—Subsequent Event. Disposition—On May 31, 2017, we completed the sale of 10 high‑specification jackups and novated the contracts relating to the construction of five high‑specification jackups, together with related assets. At December 31, 2017 we continued to operate two high‑specification jackups that were under contract when we sold the rigs, and we will continue to operate such rigs until completion or novation of the respective drilling contracts. See Note 5—Drilling Fleet.

Significant Accounting Policies	12 Months Ended
Significant Accounting Policies	Dec. 31, 2017
Significant Accounting Policies
Significant Accounting Policies	Note 2—Significant Accounting Policies Accounting estimates—To prepare financial statements in accordance with accounting principles generally accepted in the United States (“U.S.”), we are required to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosures of contingent assets and liabilities. On an ongoing basis, we evaluate our estimates and assumptions, including those related to our allowance for doubtful accounts, materials and supplies obsolescence, property and equipment, assets held for sale, income taxes, contingencies, share‑based compensation, defined benefit pension and other postemployment benefit plans. We base our estimates and assumptions on historical experience and on various other factors we believe are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying amounts of assets and liabilities that are not readily apparent from other sources. Actual results could differ from such estimates. Fair value measurements—We estimate fair value at a price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants in the principal market for the asset or liability. Our valuation techniques require inputs that we categorize using a three‑level hierarchy, from highest to lowest level of observable inputs, as follows: (1) significant observable inputs, including unadjusted quoted prices for identical assets or liabilities in active markets (“Level 1”), (2) significant other observable inputs, including direct or indirect market data for similar assets or liabilities in active markets or identical assets or liabilities in less active markets (“Level 2”) and (3) significant unobservable inputs, including those that require considerable judgment for which there is little or no market data (“Level 3”). When multiple input levels are required for a valuation, we categorize the entire fair value measurement according to the lowest level of input that is significant to the measurement even though we may have also utilized significant inputs that are more readily observable. Consolidation—We consolidate entities in which we have a majority voting interest and entities that meet the criteria for variable interest entities for which we are deemed to be the primary beneficiary for accounting purposes. We eliminate intercompany transactions and accounts in consolidation. We apply the equity method of accounting for an investment in an entity if we have the ability to exercise significant influence over the entity that (a) does not meet the variable interest entity criteria or (b) meets the variable interest entity criteria, but for which we are not deemed to be the primary beneficiary. We apply the cost method of accounting for an investment in an entity if we do not have the ability to exercise significant influence over the unconsolidated entity. We separately present within equity on our consolidated balance sheets the ownership interests attributable to parties with noncontrolling interests in our consolidated subsidiaries, and we separately present net income attributable to such parties on our consolidated statements of operations. See Note 4—Variable Interest Entities and Note 11—Noncontrolling Interest. Business combination—In connection with our acquisition of Songa, we will apply the acquisition method of accounting. Accordingly, we will record the acquired assets and assumed liabilities at fair value and recognize goodwill to the extent the fair value of the business acquired exceeds the fair value of the net assets. We will estimate the fair values of the acquired assets and assumed liabilities as of the date of the acquisition, and our estimates will be subject to adjustment based on our final assessments of the fair values of property and equipment, intangible assets, liabilities and our evaluation of tax positions and contingencies. We will complete our final assessments of the fair values of the acquired assets and assumed liabilities and our final evaluations of uncertain tax positions and contingencies within one year of the acquisition date. See Note 20—Subsequent Event. Operating revenues and expenses—We recognize operating revenues as they are realized and earned and can be reasonably measured, based on contractual dayrates, and when collectability is reasonably assured. In certain instances, when we determine that collection is not reasonably assured, we recognize revenues associated with the contract when all revenue recognition criteria have been met. In connection with drilling contracts, we may receive revenues for preparation and mobilization of equipment and personnel or for capital improvements to rigs. We defer the revenues earned and incremental costs incurred that are directly related to contract preparation and mobilization and recognize such revenues and costs over the primary contract term of the drilling project using the straight‑line method. We recognize, in operating and maintenance costs and expenses, the fees related to contract preparation and mobilization on a straight‑line basis over the estimated firm period of drilling, which is consistent with the general pace of activity, level of services being provided and dayrates being earned over the life of the contract. For contractual daily rate contracts, we recognize the losses for loss contracts as such losses are incurred. We recognize the costs of relocating drilling units without contracts to more promising market sectors as such costs are incurred. Upon completion of drilling contracts, we recognize in earnings any demobilization fees received and expenses incurred. We defer capital upgrade revenues received and recognize such revenues over the primary contract term of the drilling project. We depreciate the actual costs incurred for the capital upgrade on a straight‑line basis over the estimated useful life of the asset. We defer the periodic survey and drydock costs incurred in connection with obtaining regulatory certification to operate our rigs and well control systems on an ongoing basis, and we recognize such costs over the period until the next survey using the straight-line method. See Note 3—Accounting Standards Updates. Our other revenues represent those derived from customer contract terminations and customer reimbursable items. We recognize revenues from contract terminations as we fulfill our obligations for such terminations and when all contingencies have expired. We recognize customer reimbursable revenues as we bill our customers for reimbursement of costs associated with certain equipment, materials and supplies, subcontracted services, employee bonuses and other expenditures, resulting in little or no net effect on operating income since such recognition is concurrent with the recognition of the respective reimbursable costs in operating and maintenance expense. Share‑based compensation—To measure the fair values of stock options and stock appreciation rights granted or modified, we use the Black‑Scholes‑Merton option‑pricing model and apply assumptions for the expected life, risk‑free interest rate, dividend yield and expected volatility. To measure the fair values of granted or modified service‑based restricted share units, we use the market price of our shares on the grant date or modification date. To measure the fair values of restricted share units that are subject to performance targets, we use the market price of our shares on the measurement date for the projected number of shares expected to be earned at the end of the performance period. To measure the fair values of granted or modified restricted share units that are subject to market factors, we use a Monte Carlo simulation model and, in addition to the assumptions applied for the Black‑Scholes‑Merton option‑pricing model, we apply assumptions using a risk neutral approach and an average price at the performance start date. We recognize share‑based compensation expense in the same financial statement line item as cash compensation paid to the respective employees or non‑employee directors. For service awards, we recognize compensation expense on a straight‑line basis over the service period through the date the employee or non‑employee director is no longer required to provide service to earn the award. For performance awards with graded vesting conditions, we recognize compensation expense on a straight‑line basis over the service period for each separately vesting portion of the award as if the award was, in substance, multiple awards. In the years ended December 31, 2017, 2016 and 2015, share‑based compensation expense was $41 million, $42 million and $64 million, respectively. See Note 13—Share Based Compensation Plans. Capitalized interest—We capitalize interest costs for qualifying construction and upgrade projects and only capitalize interest costs during periods in which progress for the construction projects continues to be underway. As of December 31, 2017, we had ceased capitalization of interest costs on one uncontracted newbuild drillship due to a pause in construction in progress. In the years ended December 31, 2017, 2016 and 2015, we capitalized interest costs of $116 million, $176 million and $140 million, respectively, for our construction work in progress. Functional currency—We consider the U.S. dollar to be the functional currency for all of our operations since the majority of our revenues and expenditures are denominated in U.S. dollars, which limits our exposure to currency exchange rate fluctuations. We recognize currency exchange rate gains and losses in other, net. In the years ended December 31, 2017, 2016 and 2015, we recognized a net loss of $6 million, a net loss of $2 million and a net gain of less than $1 million, respectively, related to currency exchange rates. Income taxes—We provide for income taxes based upon the tax laws and rates in effect in the countries in which operations are conducted and income is earned. We recognize the effect of changes in tax laws as of the date of enactment. There is little or no expected relationship between the provision for or benefit from income taxes and income or loss before income taxes because the countries in which we operate have taxation regimes that vary not only with respect to nominal rate, but also in terms of the availability of deductions, credits and other benefits. Variations also arise because income earned and taxed in any particular country or countries may fluctuate from year to year. We measure deferred tax assets and liabilities using enacted tax rates that will apply in the years in which the temporary differences are expected to be recovered or paid. We record a valuation allowance for deferred tax assets when it is more likely than not that some or all of the benefit from the deferred tax asset will not be realized. In evaluating our ability to realize deferred tax assets, we consider all available positive and negative evidence, including projected future taxable income and the existence of cumulative losses in recent years. We also record a valuation allowance for deferred tax assets resulting from net operating losses incurred during the year in certain jurisdictions and for other deferred tax assets where, in our opinion, it is more likely than not that the financial statement benefit of these losses will not be realized. Additionally, we record a valuation allowance for foreign tax credit carryforwards to reflect the possible expiration of these benefits prior to their utilization. We maintain liabilities for estimated tax exposures in our jurisdictions of operation, and we recognize the provisions and benefits resulting from changes to those liabilities in our income tax expense or benefit along with related interest and penalties. Tax exposure items include potential challenges to permanent establishment positions, intercompany pricing, disposition transactions, and withholding tax rates and their applicability. These tax exposures are resolved primarily through the settlement of audits within these tax jurisdictions or by judicial means, but can also be affected by changes in applicable tax law or other factors, which could cause us to revise past estimates. See Note 6—Income Taxes. Cash and cash equivalents—We consider cash equivalents to include highly liquid debt instruments with original maturities of three months or less such as time deposits with commercial banks that have high credit ratings, U.S. Treasury and government securities, Eurodollar time deposits, certificates of deposit and commercial paper. We may also invest excess funds in no‑load, open‑ended, management investment trusts. Such management trusts invest exclusively in high‑quality money market instruments. Short‑term investments—We periodically deposit unrestricted excess funds in time deposits and commercial paper with original maturities beyond three months. Such short‑term investments are with commercial banks and companies with high credit ratings. At December 31, 2017, the carrying amount of our short‑term investments was $450 million. Accounts receivable—We earn our revenues by providing our drilling services to international oil companies and government‑owned or government‑controlled oil companies. We evaluate the credit quality of our customers on an ongoing basis, and we may occasionally require collateral or other security to support customer receivables. We establish an allowance for doubtful accounts on a case‑by‑case basis, considering changes in the financial position of a customer, when we believe the required payment of specific amounts owed to us is unlikely to occur. At December 31, 2017 and 2016, the allowance for doubtful accounts was less than $1 million. Materials and supplies—We record materials and supplies at their average cost less an allowance for obsolescence. We estimate the allowance for obsolescence based on historical experience and expectations for future use of the materials and supplies. At December 31, 2017 and 2016, the allowance for obsolescence was $141 million and $153 million, respectively. Restricted cash accounts and investments—We maintain restricted cash balances and investments that are either pledged for debt service under certain bond indentures, as required under certain bank credit arrangements, or held in accounts that are subject to restrictions due to legislation, regulation or court order. We classify such restricted cash investment balances in current assets if the restriction is expected to expire or otherwise be resolved within one year and in other assets if the restriction is expected to expire or otherwise be resolved in greater than one year. At December 31, 2017, the aggregate carrying amount of our restricted cash investments was $489 million, of which $466 million and $23 million was classified in current assets and other assets, respectively. At December 31, 2016, the aggregate carrying amount of our restricted cash investments was $510 million, of which $466 million and $44 million was classified in current assets and other assets, respectively. See Note 3—Accounting Standards Updates, Note 8—Debt and Note 10—Commitments and Contingencies. Assets held for sale—We classify an asset as held for sale when the facts and circumstances meet the criteria for such classification, including the following: (a) we have committed to a plan to sell the asset, (b) the asset is available for immediate sale, (c) we have initiated actions to complete the sale, including locating a buyer, (d) the sale is expected to be completed within one year, (e) the asset is being actively marketed at a price that is reasonable relative to its fair value, and (f) the plan to sell is unlikely to be subject to significant changes or termination. At December 31, 2017 and 2016, the aggregate carrying amount of our assets held for sale, recorded in other current assets, was $22 million and $6 million, respectively. See Note 5—Drilling Fleet. Property and equipment—The carrying amounts of our property and equipment, consisting primarily of offshore drilling rigs and related equipment, are based on our estimates, assumptions and judgments relative to capitalized costs, useful lives and salvage values of our rigs. These estimates, assumptions and judgments reflect both historical experience and expectations regarding future industry conditions and operations. At December 31, 2017, the aggregate carrying amount of our property and equipment represented approximately 78 percent of our total assets. We capitalize expenditures for newbuilds, renewals, replacements and improvements, including capitalized interest, if applicable, and we recognize the expense for maintenance and repair costs as incurred. For newbuild construction projects, we also capitalize the initial preparation, mobilization and commissioning costs incurred until the drilling unit is placed into service. Upon sale or other disposition of an asset, we recognize a net gain or loss on disposal of the asset, which is measured as the difference between the net carrying amount of the asset and the net proceeds received. We compute depreciation using the straight‑line method after allowing for salvage values. The estimated original useful lives of our drilling units range from 25 to 35 years, our buildings and improvements range from two to 30 years and our machinery and equipment range from four to 20 years. We reevaluate the remaining useful lives and salvage values of our rigs when certain events occur that directly impact the useful lives and salvage values of the rigs, including changes in operating condition, functional capability and market and economic factors. When evaluating the remaining useful lives of rigs, we also consider major capital upgrades required to perform certain contracts and the long‑term impact of those upgrades on future marketability. Long‑lived asset impairment—We review the carrying amounts of long‑lived assets, principally property and equipment, for potential impairment when events occur or circumstances change that indicate that the carrying amount of such assets may not be recoverable. For assets classified as held and used, we determine recoverability by evaluating the estimated undiscounted future net cash flows based on projected dayrates and utilization of the asset group under review. We consider our asset groups to be ultra‑deepwater floaters, harsh environment floaters, deepwater floaters and midwater floaters. When an impairment of one or more of our asset groups is indicated, we measure the impairment as the amount by which the asset group’s carrying amount exceeds its estimated fair value. We measure the fair values of our contract drilling asset groups by applying a variety of valuation methods, incorporating a combination of cost, income and market approaches, using projected discounted cash flows and estimates of the exchange price that would be received for the assets in the principal or most advantageous market for the assets in an orderly transaction between market participants as of the measurement date. For an asset classified as held for sale, we consider the asset to be impaired to the extent its carrying amount exceeds its estimated fair value less cost to sell. In the year ended December 31, 2017, we determined that the carrying amount of the midwater floater asset group exceeded its fair value, and we recognized a loss of $94 million ($93 million, or $0.25 per diluted share, net of tax) associated with the impairment of these long‑lived assets. In the year ended December 31, 2016, we determined that the carrying amount of the deepwater floater asset group exceeded its fair value, and we recognized a loss of $52 million ($0.14 per diluted share), which had no tax effect, associated with the impairment of these long‑lived assets. In the year ended December 31, 2015, we determined that the carrying amount of the deepwater floater asset group and the midwater floater asset group each exceeded its fair value, and we recognized a loss of $507 million ($481 million, or $1.31 per diluted share, net of tax) and $668 million ($654 million, or $1.78 per diluted share, net of tax) associated with the impairment of the deepwater floater asset group and the midwater floater asset group, respectively, including a loss of $52 million associated with construction in progress related to the asset groups. If we experience increasingly unfavorable changes to actual or anticipated dayrates or other impairment indicators, or if we are unable to secure new or extended contracts for our active units or the reactivation of any of our stacked units, we may be required to recognize additional losses in future periods as a result of impairments of the carrying amount of one or more of our asset groups. See Note 5—Drilling Fleet. Pension and other postemployment benefit plans—We use a measurement date of January 1 for determining net periodic benefit costs and December 31 for determining plan benefit obligations and the fair values of plan assets. We determine our net periodic benefit costs based on a market‑related value of assets that reduces year‑to‑year volatility by including investment gains or losses subject to amortization over a five‑year period from the year in which they occur. Investment gains or losses for this purpose are measured as the difference between the expected return calculated using the market‑related value of assets and the actual return based on the market‑related value of assets. If gains or losses exceed 10 percent of the greater of plan assets or plan liabilities, we amortize such gains or losses over the average expected future service period of the employee participants. We measure our actuarially determined obligations and related costs for our defined benefit pension and other postemployment benefit plans, retiree life insurance and medical benefits, by applying assumptions, including long‑term rate of return on plan assets, discount rates, mortality rates and employee turnover rates. For our defined benefit plans that have ceased accruing benefits, certain assumptions, including compensation increases and health care cost trend rates no longer apply. The two most critical assumptions are the long‑term rate of return on plan assets and the discount rate. For the long‑term rate of return, we develop our assumptions regarding the expected rate of return on plan assets based on historical experience and projected long‑term investment returns, and we weight the assumptions based on each plan’s asset allocation. For the discount rate, we base our assumptions on a yield curve approach using Aa‑rated corporate bonds and the expected timing of future benefit payments. For the projected compensation trend rate, we consider short‑term and long‑term compensation expectations for participants, including salary increases and performance bonus payments. At December 31, 2017 and 2016, our pension and other postemployment benefit plan obligations represented an aggregate liability of $359 million and $375 million, respectively, and an aggregate asset of $17 million and $5 million, respectively, representing the funded status of the plans. In the years ended December 31, 2017, 2016 and 2015, aggregate net periodic benefit costs were costs of $5 million, income of $11 million and costs of $26 million, respectively. See Note 3—Accounting Standards Updates and Note 9—Postemployment Benefit Plans. Contingencies—We perform assessments of our contingencies on an ongoing basis to evaluate the appropriateness of our liabilities and disclosures for such contingencies. We establish liabilities for estimated loss contingencies when we believe a loss is probable and the amount of the probable loss can be reasonably estimated. We recognize corresponding assets for those loss contingencies that we believe are probable of being recovered through insurance. Once established, we adjust the carrying amount of a contingent liability upon the occurrence of a recognizable event when facts and circumstances change, altering our previous assumptions with respect to the likelihood or amount of loss. We recognize expense for legal costs as they are incurred, and we recognize a corresponding asset for such legal costs only if we expect such legal costs to be recovered through insurance. Reclassifications—We have made certain reclassifications to prior period amounts to conform with the current year’s presentation. Such reclassifications did not have a material effect on our consolidated statement of financial position, results of operations or cash flows.

Accounting Standards Updates	12 Months Ended
Accounting Standards Updates	Dec. 31, 2017
Accounting Standards Updates
Accounting Standards Updates	Note 3—Accounting Standards Updates Recently adopted accounting standards Stock compensation—Effective January 1, 2017, we adopted the accounting standards update that allows for simplification of the accounting for share‑based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities and classification on the statement of cash flows. The update is effective for annual periods beginning after December 15, 2016 and interim periods within those annual periods. Our adoption did not have a material effect on our consolidated statements of financial position, operations or cash flows or on the disclosures contained in our notes to consolidated financial statements. Recently issued accounting standards Revenue from contracts with customers—Effective January 1, 2018, we will adopt the accounting standards update that requires an entity to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The update is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. Given the interaction with the accounting standards update related to leases, we expect to adopt the updates concurrently, effective January 1, 2018. We expect to apply the modified retrospective approach to our adoption, which is consistent, in application, with the approach we expect to elect under the lease accounting standards update. We have determined we have one revenue stream. Our adoption, and the ultimate effect on our consolidated financial statements, will be based on an evaluation of the contract‑specific facts and circumstances. Although we do not expect any changes to the timing of our revenue recognition for our current drilling contracts with customers, we are still evaluating the disclosures that will be contained in our note to consolidated financial statements. We are continuing to evaluate the requirements and the other effects such requirements may have on our consolidated statements of financial position, operations and cash flows and on the disclosures contained in our notes to consolidated financial statements. Leases—Effective January 1, 2018, we intend to early adopt the accounting standards update that (a) requires lessees to recognize a right to use asset and a lease liability for virtually all leases, and (b) updates previous accounting standards for lessors to align certain requirements with the updates to lessee accounting standards and the revenue recognition accounting standards. The update, which permits early adoption, is effective for interim and annual periods beginning after December 15, 2018, including interim periods within those annual periods. Under the updated definition of a lease, we have determined that our drilling contracts contain a lease component. We intend to early adopt these accounting standards, effective January 1, 2018, given the interaction with the accounting standards update related to revenue from contracts with customers. In a recent update, targeted improvements were proposed to the accounting standards that provides for (a) an optional new transition method for adoption that results in initial recognition of a cumulative effect adjustment to retained earnings in the year of adoption and (b) a practical expedient for lessors, under certain circumstances, to combine the lease and non‑lease components of revenues for presentation purposes. If the targeted improvements are approved, we intend to apply the alternative transition method, which is consistent, in application, with the approach we expect to elect under the revenue accounting standards update, and intend to elect the practical expedient for lessors for presentation purposes. Our adoption, and the ultimate effect on our consolidated financial statements, will be based on an evaluation of the contract‑specific facts and circumstances. We do not expect any changes to the timing of our revenue recognition for our current drilling contracts with customers. Additionally, based on the lease arrangements under which we are the lessee as of December 31, 2017, we expect to recognize an aggregate lease liability and a corresponding right‑to‑use asset of between $65 million and $75 million. We are continuing to evaluate the requirements with regard to arrangements under which we are the lessor and the other effects such requirements may have on our consolidated statements of financial position, operations and cash flows and on the disclosures contained in our notes to consolidated financial statements. Statement of cash flows—Effective January 1, 2018, we will adopt the accounting standards update that requires amounts generally described as restricted cash or restricted cash equivalents to be included with cash and cash equivalents when reconciling the beginning and end of period total amounts presented on the statement of cash flows. The update, which permits early adoption, is effective for annual periods beginning after December 15, 2017 and interim periods within those annual periods. Aside from presenting the restricted cash and restricted cash equivalents as a component of the beginning and ending cash balances on our consolidated statements of cash flows, we will remove the effect of proceeds from and deposits to restricted accounts from our cash flows provided by or used in operating and financing activities, as applicable. For the years ended December 31, 2017, 2016 and 2015, such changes would have resulted in an increase of $26 million, $69 million and $242 million, respectively, to cash flows provided by operating activities and for the years ended December 31, 2017 and 2016, an increase of $97 million, and $61 million, respectively, to cash flows provided by or used in financing activities. Income taxes—Effective January 1, 2018, we will adopt the accounting standards update that requires an entity to recognize the income tax consequences of an intra entity transfer of an asset other than inventory when the transaction occurs as opposed to deferring such recognition into future periods. The update, which permits early adoption, is effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual periods. We do not expect that our adoption will have a material effect on our consolidated statements of financial position, operations or cash flows or on the disclosures contained in our notes to consolidated financial statements. Retirement benefits—Effective January 1, 2018, we will adopt the accounting standards update that requires an employer to disaggregate the service cost component from the other components of net benefit cost related to defined benefit retirement plans and other postemployment benefit plans. The update requires that the service cost component be presented in the same line item as other compensation costs for employees and the other components of net benefit cost in other income and expense on our consolidated statements of operations. The update also allows only the service cost component of net benefit cost to be eligible for capitalization. The update, which permits early adoption, is effective for annual periods beginning after December 15, 2017, including interim periods within those annual periods. We do not expect that our adoption will have a material effect on our consolidated statements of cash flows or on the disclosures contained in our notes to consolidated financial statements.

Variable Interest Entities

12 Months Ended

Dec. 31, 2017

Variable Interest Entities

Variable Interest Entities

Note 4—Variable Interest Entity

Angola Deepwater Drilling Company Limited (“ADDCL”), a consolidated Cayman Islands company, is a joint venture company formed to own and operate certain drilling units. We determined that ADDCL met the criteria of a variable interest entity for accounting purposes because its equity at risk was insufficient to permit it to carry on its activities without additional subordinated financial support from us. We also determined, in each case, that we were the primary beneficiary for accounting purposes since (a) we had the power to direct the construction, marketing and operating activities, which are the activities that most significantly impact each entity’s economic performance, and (b) we had the obligation to absorb losses or the right to receive a majority of the benefits that could be potentially significant to the variable interest entity. As a result, we consolidate ADDCL in our consolidated financial statements, we eliminate intercompany transactions, and we present the interests that are not owned by us as noncontrolling interest on our consolidated balance sheets. The carrying amounts associated with ADDCL, after eliminating the effect of intercompany transactions, was as follows (in millions):


	Years ended December 31,
	2017		2016
Assets	$	716	$	787
Liabilities		7		25
Net carrying amount	$	709	$	762

Drilling Fleet

12 Months Ended

Dec. 31, 2017

Drilling Fleet

Drilling Fleet

Note 5—Drilling Fleet

Construction work in progress—For each of the three years in the period ended December 31, 2017, the changes in our construction work in progress, including capital expenditures and other capital additions, were as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Construction work in progress, at beginning of period	$	2,171	$	3,735	$	2,447

Capital expenditures
Newbuild construction program		397		1,206		1,622
Other equipment and construction projects		100		138		379
Total capital expenditures		497		1,344		2,001
Changes in accrued capital additions		(23)		(86)		(11)
Impairment of construction work in progress		—		—		(52)

Construction work in progress sold		(289)		—		—
Property and equipment placed into service
Newbuild construction program		(896)		(2,557)		—
Other property and equipment		(68)		(265)		(650)
Construction work in progress, at end of period	$	1,392	$	2,171	$	3,735

Impairments of assets held and used—During the years ended December 31, 2017, 2016 and 2015, we identified indicators that the asset groups in our contract drilling services reporting unit may not be recoverable.

In the year ended December 31, 2017, such indicators included a significant decline in commodity prices and the market value of our stock, a reduction of projected dayrates and a further extension to low utilization rates. In the year ended December 31, 2017, as a result of our testing, we recognized a loss of $94 million ($93 million, or $0.25 per diluted share, net of tax) associated with the impairment of the midwater floater asset group.

In the year ended December 31, 2016, such indicators included a reduction of projected dayrates and an extension to low utilization rates. In the year ended December 31, 2016, as a result of our testing, we recognized a loss of $52 million ($0.14 per diluted share), which had no tax effect, associated with the impairment of the deepwater floater asset group.

In the year ended December 31, 2015, such indicators included a reduction in the number of new contract opportunities, customer suspensions of drilling programs, early contract terminations and cancellations and low dayrate fixtures. In the year ended December 31, 2015, as a result of our testing, we recognized losses of $507 million ($481 million, or $1.31 per diluted share, net of tax) and $668 million ($654 million, or $1.78 per diluted share, net of tax) associated with the impairment of the deepwater floater asset group and the midwater floater asset group, respectively, including losses of $41 million and $11 million, respectively, associated with construction in progress for each asset group.

We estimated the fair value of the asset groups by applying a combination of income and market approaches, using projected discounted cash flows and estimates of the exchange price that would be received for the assets in the principal or most advantageous markets for the assets in an orderly transaction between participants as of the measurement date. Our estimates of fair value required us to use significant unobservable inputs, representative of a Level 3 fair value measurement, including assumptions related to the future performance of our contract drilling services reporting unit, such as future commodity prices, projected demand for our services, rig availability and dayrates. If we experience increasingly unfavorable changes to actual or anticipated dayrates or other impairment indicators, or if we are unable to secure new or extended contracts for our active units or the reactivation of any of our stacked units, we may be required to recognize additional losses in future periods as a result of impairments of the carrying amount of one or more of our asset groups.

Impairments of assets held for sale—In the year ended December 31, 2017, we recognized an aggregate loss of $1.4 billion ($3.59 per diluted share), which had no tax effect, associated with the impairment of the ultra‑deepwater floaters Cajun Express, Deepwater Pathfinder, GSF Jack Ryan, Sedco Energy and Sedco Express, the deepwater floater Transocean Marianas and the midwater floaters Transocean Prospect and Transocean Searcher, along with related assets, which we determined were impaired at the time that we classified the assets as assets held for sale.

In the year ended December 31, 2016, we recognized an aggregate loss of $41 million ($39 million, or $0.10 per diluted share, net of tax), associated with the impairment of the deepwater floaters M.G. Hulme, Jr. and Sedco 702 and the midwater floaters GSF Rig 140, Sedco 704, Transocean Driller, Transocean John Shaw and Transocean Winner, along with related assets, which we determined were impaired at the time that we classified the assets as assets held for sale.

In the year ended December 31, 2015, we recognized an aggregate loss of $700 million ($585 million, or $1.60 per diluted share, net of tax) associated with the impairment of the ultra‑deepwater floaters Deepwater Expedition and GSF Explorer, the deepwater floaters Deepwater Navigator, Discoverer Seven Seas, GSF Celtic Sea, Sedco 707 and Transocean Rather and the midwater floaters GSF Aleutian Key, GSF Arctic III, GSF Grand Banks, GSF Rig 135, Transocean Amirante and Transocean Legend, along with related assets, which we determined were impaired at the time that we classified the assets as assets held for sale.

We measured the impairment of the drilling units and related assets as the amount by which the carrying amount exceeded the estimated fair value less costs to sell. We estimated the fair value of the assets using significant other observable inputs, representative of Level 2 fair value measurements, including indicative market values for the drilling units and related assets based on comparable units to be sold for scrap value or alternative purposes. If we commit to plans to sell additional rigs for values below the respective carrying amounts, we may be required to recognize additional losses in future periods associated with the impairment of such assets.

Dispositions—On May 31, 2017, in connection with our efforts to dispose of non‑strategic assets, we completed the sale of 10 high‑specification jackups, including GSF Constellation I, GSF Constellation II, GSF Galaxy I, GSF Galaxy II, GSF Galaxy III, GSF Monarch, Transocean Andaman, Transocean Ao Thai, Transocean Honor and Transocean Siam Driller, along with related assets, and novated the contracts relating to the construction of five high‑specification jackups, together with related assets. In the year ended December 31, 2017, we received aggregate net cash proceeds of $319 million and recognized an aggregate net loss of $1.6 billion ($4.08 per diluted share), which had no tax effect, associated with the disposal of these assets. Following the completion of the sale, we agreed to continue to operate three of these high‑specification jackups through completion or novation of the respective drilling contracts, one of which was completed as of September 30, 2017. In the year ended December 31, 2017, excluding our loss on the disposal of these assets, our operating results included income of $65 million, before taxes, associated with the high‑specification jackup asset group. In the years ended December 31, 2016 and 2015, our operating results included income of $74 million and $208 million, respectively, before taxes, associated with the high‑specification jackup asset group.

During the year ended December 31, 2017, we also completed the sale of the ultra‑deepwater floater GSF Jack Ryan and the midwater floaters GSF Rig 140, Transocean Prospect and Transocean Searcher, along with related assets. In the year ended December 31, 2017, we received aggregate net cash proceeds of $22 million and recognized an aggregate net gain of $9 million associated with the disposal of these assets. In the year ended December 31, 2017, we received aggregate net cash proceeds of $9 million and recognized an aggregate net loss of $15 million associated with the disposal of assets unrelated to rig sales.

During the year ended December 31, 2016, in connection with our efforts to dispose of non‑strategic assets, we completed the sale of the deepwater floaters Deepwater Navigator, M.G. Hulme, Jr. and Sedco 702 and the midwater floaters Falcon 100, GSF Grand Banks, GSF Rig 135, Sedco 704, Sedneth 701, Transocean Driller, Transocean John Shaw and Transocean Winner, along with related assets. In the year ended December 31, 2016, we received aggregate net cash proceeds of $22 million and recognized an aggregate net gain of $13 million ($0.04 per diluted share, net of tax) associated with the disposal of these assets. In the year ended December 31, 2016, we received cash proceeds of $8 million and recognized an aggregate net loss of $9 million associated with the disposal of assets unrelated to rig sales.

During the year ended December 31, 2015, we completed the sale of the ultra‑deepwater floaters Deepwater Expedition and GSF Explorer, the deepwater floaters Discoverer Seven Seas, GSF Celtic Sea, Sedco 707, Sedco 710, Sovereign Explorer and Transocean Rather and the midwater floaters C. Kirk Rhein, Jr., GSF Aleutian Key, GSF Arctic I, GSF Arctic III, J.W. McLean, Sedco 601, Sedco 700, Transocean Amirante and Transocean Legend, along with related assets. In the year ended December 31, 2015, we received aggregate net cash proceeds of $35 million and recognized an aggregate net gain of $14 million ($11 million or $0.02 per diluted share, net of tax) associated with the disposal of these assets. In the year ended December 31, 2015, we received cash proceeds of $16 million and recognized an aggregate net loss of $50 million associated with the disposal of assets unrelated to rig sales.

Assets held for sale—At December 31, 2017, the aggregate carrying amount of our assets held for sale, including the ultra‑deepwater floaters Cajun Express, Deepwater Pathfinder, Sedco Energy and Sedco Express and the deepwater floater Transocean Marianas, along with related assets, was $22 million, recorded in other current assets. At December 31, 2016, the aggregate carrying amount of our assets held for sale was $6 million, including the midwater floater GSF Rig 140, along with related assets, recorded in other current assets.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Taxes

Income Taxes

Note 6—Income Taxes

Overview—Transocean Ltd., a holding company and Swiss resident, is exempt from cantonal and communal income tax in Switzerland, but is subject to Swiss federal income tax. For Swiss federal income taxes, qualifying net dividend income and net capital gains on the sale of qualifying investments in subsidiaries are exempt. Consequently, there is not a direct relationship between our Swiss earnings before income taxes and our Swiss income tax expense.

Tax provision and rate—Our provision for income taxes is based on the tax laws and rates applicable in the jurisdictions in which we operate and earn income. The relationship between our provision for or benefit from income taxes and our income or loss before income taxes can vary significantly from period to period considering, among other factors, (a) the overall level of income before income taxes, (b) changes in the blend of income that is taxed based on gross revenues rather than income before taxes, (c) rig movements between taxing jurisdictions and (d) our rig operating structures. The components of our provision (benefit) for income taxes were as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Current tax expense	$	5	$	39	$	254
Deferred tax expense (benefit)		89		68		(134)
Income tax expense	$	94	$	107	$	120

In the years ended December 31, 2017, 2016 and 2015, our effective tax rate was (3.1) percent, 11.5 percent and 11.9 percent, respectively, based on income from continuing operations before income tax expense.

The following is a reconciliation of the income tax expense (benefit) for our continuing operations computed at the Swiss holding company federal statutory rate of 7.83% and our reported provision for income taxes (in millions):


	Years ended December 31,
	2017		2016		2015

Income tax expense (benefit)	$	(235)	$	72	$	80
Impairment losses subject to rates different than the Swiss federal statutory rate		241		5		(8)
Change in valuation allowance		162		32		10
Impact of U.S. tax reform		66		—		—
Revaluation of Norwegian assets		1		18		14
Litigation matters, primarily related to the Macondo well incident		(70)		(1)		(9)
Changes in unrecognized tax benefits, net		(56)		(31)		12
Benefit from foreign tax credits		(15)		(16)		(10)
Earnings subject to rates different than the Swiss federal statutory rate		2		34		36
Other, net		(2)		(6)		(5)
Income tax expense	$	94	$	107	$	120

Deferred taxes—The significant components of our deferred tax assets and liabilities were as follows (in millions):


	December 31,
	2017		2016
Deferred tax assets
Net operating loss carryforwards	$	435	$	383
Deferred income		101		122
Accrued payroll expenses not currently deductible		54		110
Loss contingencies		42		68
Tax credit carryforwards		37		33
United Kingdom charter limitation		36		33
Professional fees		3		3
Other		30		37
Valuation allowance		(574)		(412)
Total deferred tax assets		164		377

Deferred tax liabilities
Depreciation and amortization		(157)		(239)
Other		(4)		(18)
Total deferred tax liabilities		(161)		(257)

Net deferred tax assets	$	3	$	120

At December 31, 2017 and 2016, our deferred tax assets included U.S. foreign tax credit carryforwards of $37 million and $33 million, respectively, which will expire between 2018 and 2027. The deferred tax assets related to our net operating losses were generated in various worldwide tax jurisdictions. At December 31, 2017, the net operating losses carryforwards, which were generated in various jurisdictions worldwide, included $261 million that do not expire and $174 million that will expire beginning between 2020 and 2037. At December 31, 2016, the net operating losses carryforwards, which were generated in various jurisdictions worldwide, included $200 million that do not expire and $183 million that will expire beginning 2018 and 2036. At December 31, 2017 and 2016, due to uncertainty of realization, we have recorded a valuation allowance of $574 million and $412 million, respectively, on net operating losses and other deferred tax assets.

As of December 31, 2017, our consolidated cumulative loss incurred over the recent three‑year period, primarily due to losses on impairment and disposal of assets, represented significant objective negative evidence for our evaluation. Such evidence, together with potential organizational changes that could alter our ability to realize certain deferred tax assets, has limited our ability to consider other subjective evidence, such as projected future contract activity. As a result, we recorded an incremental valuation allowance of $110 million to recognize only a portion of our U.S. deferred tax assets that are more likely than not to be recognized. If estimated future taxable income changes during the carryforward periods or if the cumulative loss is no longer present, we may adjust the amount of deferred tax assets that we expect to realize.

Our other deferred tax liabilities include taxes related to the earnings of certain subsidiaries that are not indefinitely reinvested or that will not be indefinitely reinvested in the future. We consider the earnings of certain of our subsidiaries to be indefinitely reinvested, and accordingly, we have not provided for taxes on these unremitted earnings. If we were to make a distribution from the unremitted earnings of these subsidiaries, we would be subject to taxes payable to various jurisdictions. If our expectations were to change regarding future tax consequences, we may be required to record additional deferred taxes that could have a material effect on our consolidated statement of financial position, results of operations or cash flows. Due to the timing of the enactment of the 2017 Tax Act, as discussed below, it is not practicable to estimate the amount of indefinitely reinvested earnings or the deferred tax liability related to the indefinitely reinvested earnings due to the complexities associated with the underlying hypothetical calculations.

Unrecognized tax benefits—The changes to our liabilities related to unrecognized tax benefits, excluding interest and penalties that we recognize as a component of income tax expense, were as follows (in millions):


	Years ended December 31,
		2017		2016		2015
Balance, beginning of period	$	274	$	287	$	272
Additions for prior year tax positions		17		13		17
Additions for current year tax positions		13		42		36
Reductions for prior year tax positions		(68)		(34)		(27)
Reductions related to statute of limitation expirations		(13)		(15)		(6)
Reductions due to settlements		(1)		(19)		(5)
Balance, end of period	$	222	$	274	$	287

The liabilities related to our unrecognized tax benefits, including related interest and penalties that we recognize as a component of income tax expense, were as follows (in millions):


	December 31,
		2017		2016
Unrecognized tax benefits, excluding interest and penalties	$	222	$	274
Interest and penalties		87		96
Unrecognized tax benefits, including interest and penalties	$	309	$	370

In the years ended December 31, 2017, 2016 and 2015, we recognized income of $9 million, $23 million and $1 million, respectively, recorded as a component of income tax expense, related to previously recognized interest and penalties associated with our unrecognized tax benefits. As of December 31, 2017, if recognized, $309 million of our unrecognized tax benefits, including interest and penalties, would favorably impact our effective tax rate.

It is reasonably possible that our existing liabilities for unrecognized tax benefits may increase or decrease in the year ending December 31, 2018, primarily due to the progression of open audits and the expiration of statutes of limitation. However, we cannot reasonably estimate a range of potential changes in our existing liabilities for unrecognized tax benefits due to various uncertainties, such as the unresolved nature of various audits.

U.S. tax reform—In December 2017, the U.S. enacted the Tax Cuts and Jobs Act (the “2017 Tax Act”), which includes a number of changes to existing U.S. tax laws that have an impact on our income tax provision, most notably a reduction of the U.S. corporate income tax rate from 35 percent to 21 percent for tax years beginning after December 31, 2017, and the creation of a territorial tax system with a one‑time mandatory tax on previously deferred foreign earnings of U.S. subsidiaries. The 2017 Tax Act also makes prospective changes beginning in 2018, including a base erosion and anti‑abuse tax (“BEAT”), a global intangible low‑taxed income (“GILTI”) tax, additional limitations on the deductibility of executive compensation, limitations on the deductibility of interest and repeal of the domestic manufacturing deduction. We are still evaluating the GILTI tax, which imposes a tax on non‑U.S. income in excess of a deemed return on tangible assets of non‑U.S. corporations, and its prospective effect on future periods.

We recognized the income tax effects of the 2017 Tax Act in our financial statements for the year ended December 31, 2017 in accordance with Staff Accounting Bulletin No. 118 (“SAB 118”), which provides SEC staff guidance for the application of accounting standards for income taxes in the reporting period in which the 2017 Tax Act was enacted. As such, our financial results reflect (a) the income tax effects of the 2017 Tax Act for which the accounting is complete, (b) provisional amounts for those specific income tax effects of the 2017 Tax Act for which the accounting is incomplete but a reasonable estimate could be determined and (c) no adjustments to current or deferred taxes for income tax effects for which the accounting is incomplete and a reasonable estimate could not be determined. The 2017 Tax Act’s U.S. tax law changes that we believe will have a material impact on our federal income taxes are as follows:

Reduction of the U.S. corporate income tax rate—At December 31, 2017, we remeasured our deferred tax assets and liabilities to reflect the reduction in the U.S. corporate income tax rate from 35 percent to 21 percent, resulting in a $66 million increase in income tax expense for the year ended December 31, 2017 and a corresponding $66 million decrease in net deferred tax assets as of December 31, 2017. However, we are still analyzing certain aspects of the 2017 Tax Act and refining our calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts.

Transition tax on foreign earnings—The 2017 Tax Act imposes a one‑time transition tax on certain unremitted earnings and profits of the foreign subsidiaries of our U.S. subsidiaries. Prior to enactment of the 2017 Tax Act, we did not recognize a deferred tax liability related to the unremitted earnings of the foreign subsidiaries of our U.S. subsidiaries because we considered those foreign earnings to be indefinitely reinvested. Upon enactment of the 2017 Tax Act, we did not have the necessary information available, prepared and analyzed to develop a reasonable estimate of the transition tax. We have not yet completed our calculation of the post‑1986 earnings and profits for the foreign subsidiaries of our U.S. subsidiaries or determined the amounts of those earnings held in cash and other assets necessary to determine the transition tax. The determination of the transition tax requires further analysis regarding the amount and composition of our historical foreign earnings, which is expected to be completed and reflected in our financial statements issued for subsequent reporting periods that fall within the measurement period provided by SAB 118. The transition tax will also impact the utilization of our foreign tax credits and net operating losses generated in the U.S. which will impact our valuation allowance analysis related to those deferred tax assets and could have a material impact to our valuation allowances. Because we have not completed our analysis of the amount and composition of our historical foreign earnings and the associated transition tax, we also cannot determine the associated impact on our assertion that the unremitted earnings of the foreign subsidiaries of our U.S. subsidiaries will be indefinitely reinvested.

Tax returns—We file federal and local tax returns in several jurisdictions throughout the world. With few exceptions, we are no longer subject to examinations of our U.S. and non‑U.S. tax matters for years prior to 2010. Our tax returns in the major jurisdictions in which we operate, other than Brazil, as mentioned below, are generally subject to examination for periods ranging from three to six years. We have agreed to extensions beyond the statute of limitations in two major jurisdictions for up to 20 years. Tax authorities in certain jurisdictions are examining our tax returns and in some cases have issued assessments. We are defending our tax positions in those jurisdictions. While we cannot predict or provide assurance as to the timing or the outcome of these proceedings, we do not expect the ultimate liability to have a material adverse effect on our consolidated statement of financial position or results of operations, although it may have a material adverse effect on our consolidated statement of cash flows.

Brazil tax investigations—In December 2005, the Brazilian tax authorities issued a tax assessment with respect to our tax returns for the years 2000 through 2004, which is currently for an aggregate amount of BRL 853 million, equivalent to approximately $258 million, including penalties and interest. On January 25, 2008, we filed a protest letter with the Brazilian tax authorities for this tax assessment, and we are currently engaged in the appeals process. On May 19, 2014, the Brazilian tax authorities issued an aggregate tax assessment with respect to our Brazilian income tax returns for the years 2009 and 2010, which is currently for an aggregate amount of BRL 145 million, equivalent to approximately $44 million, including penalties and interest. On June 18, 2014, we filed a protest letter with the Brazilian tax authorities for this tax assessment. We believe our returns are materially correct as filed, and we are vigorously contesting these assessments. An unfavorable outcome on these proposed assessments could result in a material adverse effect on our consolidated statement of financial position, results of operations or cash flows.

Other tax matters—We conduct operations through our various subsidiaries in a number of countries throughout the world. Each country has its own tax regimes with varying nominal rates, deductions, employee contribution requirements and tax attributes. From time to time, we may identify changes to previously evaluated tax positions that could result in adjustments to our recorded assets and liabilities. Although we are unable to predict the outcome of these changes, we do not expect the effect, if any, resulting from these adjustments to have a material adverse effect on our consolidated statement of financial position, results of operations or cash flows.

Earnings (Loss) Per Share

12 Months Ended

Dec. 31, 2017

Earnings (Loss) Per Share

Earnings (Loss) Per Share

Note 7—Earnings (Loss) Per Share

The numerator and denominator used for the computation of basic and diluted per share earnings from continuing operations were as follows (in millions, except per share data):


	Years ended December 31,
	2017				2016				2015
	Basic		Diluted		Basic		Diluted		Basic		Diluted
Numerator for earnings (loss) per share
Income (loss) from continuing operations attributable to controlling interest	$	(3,127)	$	(3,127)	$	778	$	778	$	865	$	865
Undistributed earnings allocable to participating securities		—		—		(14)		(14)		(8)		(8)
Income (loss) from continuing operations available to shareholders	$	(3,127)	$	(3,127)	$	764	$	764	$	857	$	857

Denominator for earnings (loss) per share
Weighted-average shares outstanding		391		391		367		367		363		363
Effect of stock options and other share-based awards		—		—		—		—		—		—
Weighted-average shares for per share calculation		391		391		367		367		363		363

Per share earnings (loss) from continuing operations	$	(8.00)	$	(8.00)	$	2.08	$	2.08	$	2.36	$	2.36

In the years ended December 31, 2017, 2016 and 2015, we excluded from the calculation 4.7 million, 2.5 million and 3.3 million share‑based awards, respectively, since the effect would have been anti‑dilutive.

Debt

12 Months Ended

Dec. 31, 2017

Debt

Debt

Note 8—Debt

Overview

Outstanding debt—The aggregate principal amounts and aggregate carrying amounts, net of debt‑related balances, including unamortized discounts, premiums, issue costs and fair value adjustments, of our debt were as follows (in millions):


	Principal amount				Carrying amount
	December 31,		December 31,		December 31,		December 31,
	2017		2016		2017		2016
2.50% Senior Notes due October 2017 (a)	$	—	$	485	$	—	$	484
Eksportfinans Loans due January 2018		26		123		26		123
6.00% Senior Notes due March 2018 (a)		—		754		—		757
7.375% Senior Notes due April 2018 (a)		—		211		—		211
6.50% Senior Notes due November 2020 (a)		286		508		288		513
6.375% Senior Notes due December 2021 (a)		328		552		327		549
5.52% Senior Secured Notes due May 2022 (b)		362		—		356		—
3.80% Senior Notes due October 2022 (a)		506		539		502		534
9.00% Senior Notes due July 2023 (c)		1,250		1,250		1,216		1,211
7.75% Senior Secured Notes due October 2024 (d)		540		600		526		583
6.25% Senior Secured Notes due December 2024 (d)		562		625		549		609
7.50% Senior Notes due January 2026 (c)		750		—		742		—
7.45% Notes due April 2027 (a)		88		88		86		86
8.00% Debentures due April 2027 (a)		57		57		57		57
7.00% Notes due June 2028		300		300		307		308
Capital lease contract due August 2029		541		566		541		566
7.50% Notes due April 2031 (a)		588		588		585		585
6.80% Senior Notes due March 2038 (a)		1,000		1,000		991		991
7.35% Senior Notes due December 2041 (a)		300		300		297		297
Total debt		7,484		8,546		7,396		8,464
Less debt due within one year
2.50% Senior Notes due October 2017 (a)		—		485		—		484
Eksportfinans Loans due January 2018		26		98		26		98
5.52% Senior Secured Notes due May 2022 (b)		79		—		77		—
7.75% Senior Secured Notes due October 2024 (b)		60		60		57		57
6.25% Senior Secured Notes due December 2024 (b)		62		63		60		60
Capital lease contract due August 2029		30		25		30		25
Total debt due within one year		257		731		250		724
Total long-term debt	$	7,227	$	7,815	$	7,146	$	7,740

(a)

Transocean Inc., a 100 percent owned direct subsidiary of Transocean Ltd., is the issuer of the notes and debentures. Transocean Ltd. has provided a full and unconditional guarantee of the notes and debentures and borrowings under an unsecured five‑year revolving credit facility (see “Five‑Year Revolving Credit Facility”). Transocean Ltd. has no independent assets or operations, and its other subsidiaries not owned indirectly through Transocean Inc. were minor. Transocean Inc. has no independent assets and operations, other than those related to its investments in non‑guarantor operating companies and balances primarily pertaining to its cash and cash equivalents and debt. Except as discussed under “Indentures,” Transocean Ltd. and Transocean Inc. are not subject to any significant restrictions on their ability to obtain funds from their consolidated subsidiaries by dividends, loans or capital distributions.

(b)

The subsidiary issuer of the unregistered senior secured notes is a wholly owned indirect subsidiary of Transocean Inc. The senior secured notes are fully and unconditionally guaranteed by the owner of the collateral rig. See “—Debt issuances—Senior secured notes.”

(c)

Transocean Inc. is the issuer of the unregistered notes. The priority guaranteed senior unsecured notes, which rank equal in right of payment of all of our existing and future unsecured unsubordinated obligations and rank structurally senior to the extent of the value of the assets of the subsidiaries guaranteeing the notes, are fully and unconditionally, jointly and severally, guaranteed by Transocean Ltd. and certain wholly owned subsidiaries of Transocean Inc. See “—Debt issuances—Priority guaranteed senior unsecured notes.”

(d)

Each subsidiary issuer of the respective unregistered senior secured notes is a wholly owned indirect subsidiary of Transocean Inc. The senior secured notes are fully and unconditionally, jointly and severally, guaranteed by Transocean Ltd., Transocean Inc. and, in each case, the owner of the respective collateral rig. See “—Debt issuances—Senior secured notes.”

Scheduled maturities—At December 31, 2017, the scheduled maturities of our debt were as follows (in millions):


	Total
Years ending December 31,
2018	$	257
2019		237
2020		531
2021		580
2022		687
Thereafter		5,192
Total principal amount of debt		7,484
Total debt-related balances, net		(88)
Total carrying amount of debt	$	7,396

Indentures—The indentures that govern our debt contain covenants that, among other things, limit our ability to incur certain liens on our drilling units without equally and ratably securing the notes, to engage in certain sale and lease back transactions covering any of our drilling units, to allow our subsidiaries to incur certain additional debt, or to engage in certain merger, consolidation or reorganization transactions or to enter into a scheme of arrangement qualifying as an amalgamation. Additionally, the indentures that govern the 5.52% senior secured notes due May 2022 (the “5.52% Senior Secured Notes”), the 7.75% senior secured notes due October 2024 (the “7.75% Senior Secured Notes”) and the 6.25% senior secured notes due December 2024 (the “6.25% Senior Secured Notes” and, collectively with the 5.52% Senior Secured Notes and the 7.75% Senior Secured Notes, the “Senior Secured Notes”) contain covenants that limit the ability of our subsidiaries that own or operate the collateral rigs to declare or pay dividends to their affiliates. The 7.75% Senior Secured Notes and the 6.25% Senior Secured Notes also impose a maximum collateral rig leverage ratio (“Maximum Collateral Ratio”), represented by each rig’s earnings relative to the debt balance, that changes over the terms of the notes. At December 31, 2017, the Maximum Collateral Ratio under both indentures was less than 5.75 to 1.00. See Note 10—Commitments and Contingencies—Global Marine litigation.

Interest rate adjustments—The interest rates for certain of our notes are subject to adjustment from time to time upon a change to the credit rating of our non‑credit enhanced senior unsecured long‑term debt (“Debt Rating”). At December 31, 2017, based on our Debt Rating on that date, the interest rate in effect for the 2.50% senior notes due October 2017 (the “2.50% Senior Notes”) and the 3.80% senior notes due October 2022 was 4.50 percent and 5.80 percent, respectively, and the interest rate in effect for the 6.375% senior notes due December 2021 and the 7.35% senior notes due December 2041 was 8.375 percent and 9.35 percent, respectively.

Five‑Year Revolving Credit Facility—In June 2014, we entered into an amended and restated bank credit agreement, which established a $3.0 billion unsecured five‑year revolving credit facility, which is scheduled to expire on June 28, 2019 (the “Five‑Year Revolving Credit Facility”). Among other things, the Five‑Year Revolving Credit Facility includes limitations on creating liens, incurring subsidiary debt, transactions with affiliates, sale/leaseback transactions, mergers and the sale of substantially all assets. The Five‑Year Revolving Credit Facility also includes a covenant imposing a maximum consolidated indebtedness to total tangible capitalization ratio of 0.6 to 1.0. Borrowings under the Five‑Year Revolving Credit Facility are subject to acceleration upon the occurrence of an event of default. Additionally, such borrowings are guaranteed by Transocean Ltd. and may be prepaid in whole or in part without premium or penalty.

We may borrow under the Five‑Year Revolving Credit Facility at either (1) the adjusted London Interbank Offered Rate (“LIBOR”) plus a margin (the “Five‑Year Revolving Credit Facility Margin”), which ranges from 1.125 percent to 2.0 percent based on the Debt Rating, or (2) the base rate specified in the credit agreement plus the Five‑Year Revolving Credit Facility Margin, less one percent per annum. Throughout the term of the Five‑Year Revolving Credit Facility, we pay a facility fee on the daily unused amount of the underlying commitment which ranges from 0.15 percent to 0.35 percent based on our Debt Rating. At December 31, 2017, based on our Debt Rating on that date, the Five‑Year Revolving Credit Facility Margin was 2.0 percent and the facility fee was 0.35 percent. At December 31, 2017, we had no borrowings outstanding, $7 million of letters of credit issued, and we had $3.0 billion of available borrowing capacity under the Five‑Year Revolving Credit Facility. See Note 10—Commitments and Contingencies—Global Marine litigation.

Debt issuances

Priority guaranteed senior unsecured notes—On October 17, 2017, we completed an offering of an aggregate principal amount of $750 million of 7.50% senior unsecured notes due January 15, 2026 (the “7.50% Senior Notes”), and we received aggregate cash proceeds of $742 million, net of issue costs. We are required to pay interest on the 7.50% Senior Notes semiannually on January 15 and July 15 of each year, beginning on July 15, 2018. We may redeem all or a portion of the 7.50% Senior Notes at any time prior to January 15, 2021 at a price equal to 100 percent of the aggregate principal amount plus a make‑whole provision, and on or after January 15, 2021, at specified redemption prices.

On July 21, 2016, we completed an offering of an aggregate principal amount of $1.25 billion of 9.00% senior unsecured notes due July 15, 2023 (the “9.00% Senior Notes”), and we received aggregate cash proceeds of $1.21 billion, net of initial discount and costs payable by us. We are required to pay interest on the 9.00% Senior Notes semiannually on January 15 and July 15 of each year. We may redeem all or a portion of the 9.00% Senior Notes at any time prior to July 15, 2020 at a price equal to 100 percent of the aggregate principal amount plus a make‑whole provision, and on or after July 15, 2020, at specified redemption prices.

Senior secured notes—On May 5, 2017, we completed an offering of an aggregate principal amount of $410 million of 5.52% Senior Secured Notes, and we received aggregate cash proceeds of $403 million, net of issue costs. We are required to pay quarterly installments of principal and interest on the last business day of March, June, September and December of each year. We may redeem all or a portion of the 5.52% Senior Secured Notes at any time on or prior to December 31, 2021 at a price equal to 100 percent of the aggregate principal amount plus, subject to certain exceptions related to the drilling contract for Deepwater Conqueror, a make‑whole amount. We will be required to redeem or to offer to redeem the notes at a price equal to 100 percent of the aggregate principal amount, and, under certain circumstances, the payment of a make‑whole amount, upon the occurrence of certain events related to Deepwater Conqueror and the related drilling contract.

On October 19, 2016, we completed an offering of an aggregate principal amount of $600 million of 7.75% Senior Secured Notes, and we received aggregate cash proceeds of $583 million, net of initial discount and issue costs. On December 8, 2016, we completed an offering of an aggregate principal amount of $625 million of 6.25% Senior Secured Notes, and we received aggregate cash proceeds of $609 million, net of initial discount and issue costs. We are required to pay semiannual installments of principal and interest on the 7.75% Senior Secured Notes on April 15 and October 15 of each year, and we are required to pay semiannual installments of principal and interest on the 6.25% Senior Secured Notes on June 1 and December 1 of each year. We may redeem all or a portion of the 7.75% Senior Secured Notes and the 6.25% Senior Secured Notes at any time on or prior to October 15, 2020 and December 1, 2020, respectively, at a price equal to 100 percent of the aggregate principal amount plus a make‑whole provision. We will be required to redeem the notes at a price equal to 100 percent of the aggregate principal amount, without a make‑whole provision, upon the occurrence of certain events related to the collateral rig and the related drilling contract.

The 5.52% Senior Secured Notes are secured by the assets and earnings associated with the ultra‑deepwater floater Deepwater Conqueror, the equity of the wholly owned subsidiaries that own and operate the collateral rig, and certain related assets. The 7.75% Senior Secured Notes are secured by the assets and earnings associated with the ultra‑deepwater floater Deepwater Thalassa and the equity of the wholly owned subsidiary that owns the collateral rig. The 6.25% Senior Secured Notes are secured by the assets and earnings associated with the ultra‑deepwater floater Deepwater Proteus and the equity of the subsidiary that owns the collateral rig. At December 31, 2017 and 2016, we had $211 million and $103 million, respectively, deposited in restricted cash accounts to satisfy debt service and working capital requirements for the Senior Secured Notes. At December 31, 2017, the aggregate carrying amount of Deepwater Conqueror, Deepwater Thalassa and Deepwater Proteus was $2.4 billion. At December 31, 2016, the aggregate carrying amount of Deepwater Thalassa and Deepwater Proteus was $1.7 billion.

Debt retirement

Tender offers—On July 11, 2017, we completed cash tender offers to purchase up to $1.5 billion aggregate principal amount of certain notes (the “2017 Tendered Notes”). On August 1, 2016, we completed cash tender offers to purchase up to $1.0 billion aggregate principal amount of certain notes (the “2016 Tendered Notes”). During the years ended December 31, 2017 and 2016, we received valid tenders from holders of an aggregate principal amount of the 2017 Tendered Notes and the 2016 Tendered Notes as follows (in millions):



	Years ended
	December 31,
	2017			2016

2.50% Senior Notes due October 2017	$	271	$	—
6.00% Senior Notes due March 2018		400		—
7.375% Senior Notes due April 2018		128		—
6.50% Senior Notes due November 2020		207		348
6.375% Senior Notes due December 2021		213		476
3.80% Senior Notes due October 2022		—		157
Aggregate principal amount retired	$	1,219	$	981

Aggregate cash payment	$	1,269	$	876
Aggregate net gain (loss)	$	(48)	$	104

Repurchases and redemptions—During the years ended December 31, 2017, 2016 and 2015, we repurchased in the open market or redeemed debt securities with aggregate principal amounts as follows (in millions):


	Years ended December 31,
		2017		2016		2015

4.95% Senior Notes due November 2015	$	—	$	—	$	893
5.05% Senior Notes due December 2016		—		36		25
2.50% Senior Notes due October 2017		62		85		180
6.00% Senior Notes due March 2018		354		35		211
7.375% Senior Notes due April 2018		83		26		10
6.50% Senior Notes due November 2020		15		44		—
6.375% Senior Notes due December 2021		10		122		50
3.80% Senior Notes due October 2022		33		38		16
7.45% Notes due April 2027		—		8		4
7.50% Notes due April 2031		—		5		7
Aggregate principal amount retired	$	557	$	399	$	1,396

Aggregate cash payment	$	564	$	354	$	1,372
Aggregate net gain (loss)	$	(7)	$	44	$	23

Scheduled maturities and installments—On the scheduled maturity date of October 16, 2017, we made a cash payment of $152 million to repay the outstanding 2.50% Senior Notes, at a price equal to 100 percent of the aggregate principal amount. On the scheduled maturity date of December 15, 2016, we made a cash payment of $938 million to repay the outstanding 5.05% senior notes due December 2016, at a price equal to 100 percent of the aggregate principal amount. In the years ended December 31, 2017, 2016 and 2015, we also made cash payments of $299 million, $127 million and $134 million to repay other indebtedness in scheduled installments.

Postemployment Benefit Plans

12 Months Ended

Dec. 31, 2017

Postemployment Benefit Plans

Postemployment Benefit Plans

Note 9—Postemployment Benefit Plans

Defined benefit pension and other postemployment benefit plans

Overview—As of December 31, 2017, we had defined benefit plans in the U.S., the United Kingdom (“U.K.”), and Norway. Benefits under the defined benefit plans in the U.S. and the U.K. have ceased accruing. We maintain the respective pension obligations under such plans until they have been fully satisfied. As of December 31, 2017, the defined benefit plans in the U.S. included three funded and three unfunded plans (the “U.S. Plans”). During the year ended December 31, 2016, we permitted certain participants of one of our funded U.S. Plans to make a one‑time election to receive a payment of retirement benefits in the form of either (a) a lump sum distribution or (b) an annuity starting October 1, 2016.

As of December 31, 2017, the defined benefit plan in the U.K. included one funded plan (the “U.K. Plan”). During the year ended December 31, 2017, we permitted certain participants to make a one‑time election to receive payment of retirement benefits in the form of a lump sum distribution. As of December 31, 2017, the defined benefit plans in Norway, primarily group pension schemes with life insurance companies, included two funded and two unfunded plans, (the “Norway Plans”). During the year ended December 31, 2016, we satisfied our obligations under four funded defined benefit plans in Norway and an unfunded defined benefit plan in Nigeria. During the year ended December 31, 2015, we satisfied our obligations under unfunded defined benefit plans in Egypt and Indonesia. We refer to the U.K. Plan, the Norway Plans and the plans in Nigeria, Egypt and Indonesia, collectively, as the “Non‑U.S. Plans.”

We refer to the U.S. Plans and the Non‑U.S. Plans, collectively, as the “Transocean Plans”. Additionally, we maintain certain unfunded other postemployment benefit plans (collectively, the “OPEB Plans”), under which benefits to eligible participants diminish during a phase‑out period ending December 31, 2025.

Assumptions—We estimated our benefit obligations using the following weighted‑average assumptions:


	December 31, 2017						December 31, 2016
	U.S.		Non-U.S.		OPEB		U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Plans		Plans		Plans
Discount rate	3.68	%	2.49	%	2.93	%	4.26	%	2.69	%	3.08	%
Compensation trend rate	na		2.50	%	na		na		2.25	%	na

We estimated our net periodic benefit costs using the following weighted‑average assumptions:


	Year ended December 31, 2017						Year ended December 31, 2016						Year ended December 31, 2015
	U.S.		Non-U.S.		OPEB		U.S.		Non-U.S.		OPEB		U.S.		Non-U.S.
	Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans		OPEB Plans
Discount rate	4.26	%	2.69	%	3.08	%	4.56	%	3.69	%	3.13	%	4.16	%	3.26	%	3.86	%
Expected rate of return	6.31	%	4.79	%	na		6.82	%	5.85	%	na		7.79	%	5.93	%	na
Compensation trend rate	na	%	2.25	%	na		0.22	%	4.01	%	na		0.21	%	3.83	%	na
Health care cost trend rate
-initial	na		na		na		na		na		na		na		na		7.81	%
-ultimate	na		na		na		na		na		na		na		na		5.00	%
-ultimate year	na		na		na		na		na		na		na		na		2023

“na” means not applicable.

Net periodic benefit costs—Net periodic benefit costs, before tax, included the following components (in millions):


	Year ended December 31, 2017						Year ended December 31, 2016						Year ended December 31, 2015
	U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean
	Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans
Net periodic benefit costs
Service cost	$	3	$	3	$	6	$	3	$	10	$	13	$	5	$	26	$	31
Interest cost		65		11		76		69		17		86		65		19		84
Expected return on plan assets		(74)		(20)		(94)		(80)		(25)		(105)		(87)		(28)		(115)
Settlements and curtailments		—		13		13		—		(5)		(5)		3		2		5
Actuarial (gain) loss, net		5		1		6		5		(1)		4		11		11		22
Prior service cost, net		—		—		—		—		—		—		—		—		—
Net periodic benefit costs	$	(1)	$	8	$	7	$	(3)	$	(4)	$	(7)	$	(3)	$	30	$	27

In the years ended December 31, 2017, 2016 and 2015, for the OPEB Plans, the combined components of net periodic benefit costs, including service cost, interest cost, recognized net actuarial losses, prior service cost amortization, curtailments and special termination benefits, were income of $2 million, income of $4 million and income of $1 million, respectively.

The following table presents the amounts in accumulated other comprehensive income (loss), before tax, that have not been recognized as components of net periodic benefit costs (in millions):


	December 31, 2017								December 31, 2016
	U.S.		Non-U.S.		OPEB				U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total		Plans		Plans		Plans		Total
Actuarial gain (loss), net	$	(301)	$	(84)	$	(4)	$	(389)	$	(316)	$	(94)	$	(3)	$	(413)
Prior service cost, net		—		—		23		23		—		—		26		26
Total	$	(301)	$	(84)	$	19	$	(366)	$	(316)	$	(94)	$	23	$	(387)

The following table presents the amounts in accumulated other comprehensive income expected to be recognized as components of net periodic benefit costs during the year ending December 31, 2018 (in millions):


	Year ending December 31, 2018
	U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total
Actuarial loss, net	$	7	$	1	$	1	$	9
Prior service cost, net		—		—		(3)		(3)
Total amount expected to be recognized	$	7	$	1	$	(2)	$	6

Funded status—The changes in projected benefit obligation, plan assets and funded status and the amounts recognized on our consolidated balance sheets were as follows (in millions):


	Year ended December 31, 2017								Year ended December 31, 2016
	U.S.		Non-U.S.		OPEB				U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total		Plans		Plans		Plans		Total
Change in projected benefit obligation
Projected benefit obligation, beginning of period	$	1,557	$	398	$	19	$	1,974	$	1,523	$	502	$	24	$	2,049
Actuarial (gains) losses, net		115		18		2		135		52		36		(3)		85
Service cost		3		3		—		6		3		10		—		13
Interest cost		65		11		—		76		69		17		1		87
Currency exchange rate changes		—		35		—		35		—		(77)		—		(77)
Participant contributions		—		—		—		—		—		—		1		1
Benefits paid		(60)		(86)		(2)		(148)		(90)		(46)		(4)		(140)
Settlements and curtailments		—		—		—		—		—		(44)		—		(44)
Projected benefit obligation, end of period		1,680		379		19		2,078		1,557		398		19		1,974

Change in plan assets
Fair value of plan assets, beginning of period		1,204		400		—		1,604		1,198		439		—		1,637
Actual return on plan assets		198		31		—		229		93		84		—		177
Currency exchange rate changes		—		36		—		36		—		(80)		—		(80)
Employer contributions		1		12		2		15		3		43		3		49
Participant contributions		—		—		—		—		—		—		1		1
Benefits paid		(60)		(86)		(2)		(148)		(90)		(46)		(4)		(140)
Settlements		—		—		—		—		—		(40)		—		(40)
Fair value of plan assets, end of period		1,343		393		—		1,736		1,204		400		—		1,604

Funded status, end of period	$	(337)	$	14	$	(19)	$	(342)	$	(353)	$	2	$	(19)	$	(370)

Balance sheet classification, end of period:
Pension asset, non-current	$	—	$	17	$	—	$	17	$	—	$	5	$	—	$	5
Pension liability, current		(2)		(1)		(3)		(6)		(2)		—		(3)		(5)
Pension liability, non-current		(335)		(2)		(16)		(353)		(351)		(3)		(16)		(370)
Accumulated other comprehensive income (loss) (a)		(301)		(84)		19		(366)		(316)		(94)		23		(387)

(a)

Amounts are before income tax effect.

The aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets were as follows (in millions):


	December 31, 2017								December 31, 2016
	U.S.		Non-U.S.		OPEB				U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total		Plans		Plans		Plans		Total
Projected benefit obligation	$	1,680	$	5	$	19	$	1,704	$	1,557	$	5	$	19	$	1,581
Fair value of plan assets		1,343		2		—		1,345		1,204		2		—		1,206

At December 31, 2017 and 2016, the accumulated benefit obligation for all defined benefit pension plans was $2.1 billion and $2.0 billion, respectively. The aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets were as follows (in millions):


	December 31, 2017								December 31, 2016
	U.S.		Non-U.S.		OPEB				U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total		Plans		Plans		Plans		Total
Accumulated benefit obligation	$	1,680	$	3	$	19	$	1,702	$	1,557	$	4	$	19	$	1,580
Fair value of plan assets		1,343		—		—		1,343		1,204		—		—		1,204

Plan assets—We periodically review our investment policies, plan assets and asset allocation strategies to evaluate performance relative to specified objectives. In determining our asset allocation strategies for the U.S. Plans, we review the results of regression models to assess the most appropriate target allocation for each plan, given the plan’s status, demographics and duration. For the U.K. Plan, the plan trustees establish the asset allocation strategies consistent with the regulations of the U.K. pension regulators and in consultation with financial advisors and company representatives. Investment managers for the U.S. Plans and the U.K. Plan are given established ranges within which the investments may deviate from the target allocations. For the Norway Plans, we establish minimum rates of return under the terms of investment contracts with insurance companies.

As of December 31, 2017 and 2016, the weighted‑average target and actual allocations of the investments for our funded Transocean Plans were as follows:


	December 31, 2017									December 31, 2016
		Target allocation				Actual allocation				Target allocation				Actual allocation
		U.S.		Non-U.S.		U.S.		Non-U.S.		U.S.		Non-U.S.		U.S.		Non-U.S.
		Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans
Equity securities		50	%	39	%	52	%	39	%	50	%	45	%	53	%	45	%
Fixed income securities		50	%	50	%	48	%	48	%	50	%	45	%	47	%	44	%
Other investments		—		11	%	—		13	%	—		10	%	—	%	11	%
Total		100	%	100	%	100	%	100	%	100	%	100	%	100	%	100	%

As of December 31, 2017, the investments for our funded Transocean Plans were categorized as follows (in millions):


	December 31, 2017
	Significant observable inputs						Significant other observable inputs						Total
	U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean
	Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans
Mutual funds
U.S. equity funds	$	557	$	—	$	557	$	—	$	—	$	—	$	557	$	—	$	557
Non-U.S. equity funds		138		—		138		5		153		158		143		153		296
Bond funds		629		—		629		8		190		198		637		190		827
Total mutual funds		1,324		—		1,324		13		343		356		1,337		343		1,680

Other investments
Cash and money market funds		6		7		13		—		—		—		6		7		13
Property collective trusts		—		—		—		—		20		20		—		20		20
Investment contracts		—		—		—		—		23		23		—		23		23
Total other investments		6		7		13		—		43		43		6		50		56

Total investments	$	1,330	$	7	$	1,337	$	13	$	386	$	399	$	1,343	$	393	$	1,736

As of December 31, 2016, the investments for our funded Transocean Plans were categorized as follows (in millions):


	December 31, 2016
	Significant observable inputs						Significant other observable inputs						Total
	U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean
	Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans
Mutual funds
U.S. equity funds	$	516	$	—	$	516	$	2	$	—	$	2	$	518	$	—	$	518
Non-U.S. equity funds		113		—		113		4		181		185		117		181		298
Bond funds		567		—		567		—		178		178		567		178		745
Total mutual funds		1,196		—		1,196		6		359		365		1,202		359		1,561

Other investments
Cash and money market funds		2		2		4		—		—		—		2		2		4
Property collective trusts		—		—		—		—		17		17		—		17		17
Investment contracts		—		—		—		—		22		22		—		22		22
Total other investments		2		2		4		—		39		39		2		41		43

Total investments	$	1,198	$	2	$	1,200	$	6	$	398	$	404	$	1,204	$	400	$	1,604

The U.S. Plans and the U.K. Plan invest primarily in passively managed funds that reference market indices. The funded Norway Plans are subject to contractual terms under selected insurance programs. Each plan’s investment managers have discretion to select the securities held within each asset category. Given this discretion, the managers may occasionally invest in our debt or equity securities, and may hold either long or short positions in such securities. As the plan investment managers are required to maintain well diversified portfolios, the actual investment in our securities would be immaterial relative to asset categories and the overall plan assets.

Funding contributions—In the years ended December 31, 2017, 2016 and 2015, we made an aggregate contribution of $15 million, $49 million and $39 million, respectively, to the Transocean Plans and the OPEB Plans using our cash flows from operations. In the year ending December 31, 2018, we expect to contribute $12 million to the Transocean Plans, and we expect to fund benefit payments of approximately $3 million for the OPEB Plans as costs are incurred.

Benefit payments—The following were the projected benefits payments (in millions):


	U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total
Years ending December 31,
2018	$	71	$	8	$	3	$	82
2019		73		7		3		83
2020		75		8		3		86
2021		79		8		2		89
2022		80		9		2		91
2023 - 2027		421		60		7		488

Defined contribution plans

At December 31, 2017, we sponsored four defined contribution plans, including (1) a qualified savings plan covering certain employees working in the U.S. (the “U.S. Savings Plan”), (2) a non‑qualified supplemental plan covering certain eligible employees working in the U.S. (the “U.S. Savings Restoration Plan”), (3) a qualified savings plan covering certain eligible U.K. employees (the “U.K. Savings Plan”) and (4) a non‑qualified savings plan covering certain employees working outside the U.S. and U.K. (the “Non‑U.S. Savings Plan”). In the years ended December 31, 2017, 2016 and 2015, we recognized expense of $43 million, $51 million and $89 million, respectively, related to our defined contribution plans.

The U.S. Savings Plan provides eligible employees with matching contributions up to 10.0 percent of each participant’s base salary and annual bonus based on the participant’s contribution to the plan. The U.S. Savings Restoration Plan provides eligible employees with benefits in excess of those allowed under the U.S. Savings Plan.

The U.K. Savings Plan provides eligible employees with matching contributions between 4.5 percent and 9.5 percent based on the participant’s contribution to the plan. Effective January 1, 2017, the Non‑U.S. Savings Plan, provides eligible employees with matching contributions up to 12 percent of each participant’s base salary based on the participant’s contribution to the plan. In the years ended December 31, 2016 and 2015, the Non‑U.S. Savings Plan provided eligible employees with matching contributions up to 6.0 percent and contributions between 4.5 percent and 6.5 percent of each participant’s base salary and annual bonus based on the participant’s years of eligible service.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies

Commitments and Contingencies

Note 10—Commitments and Contingencies

Lease obligations

We have operating lease obligations expiring at various dates, principally for real estate, office space and operating equipment. In the years ended December 31, 2017, 2016 and 2015, our rental expense for all operating leases, including operating leases with terms of less than one year, was approximately $52 million, $45 million and $72 million, respectively.

We also have a capital lease obligation, which is due to expire in August 2029. The capital lease contract has an implicit interest rate of 7.8 percent and requires scheduled monthly payments of $6 million through August 2029, after which we will have the right and obligation to acquire the drillship from the lessor for one dollar. In the years ended December 31, 2017, 2016 and 2015, depreciation expense associated with Petrobras 10000, the asset held under capital lease, was $23 million. At December 31, 2017 and 2016, the aggregate carrying amount of this asset held under capital lease was as follows (in millions):


	December 31,
		2017	2016
Property and equipment, cost	$	774	$	776
Accumulated depreciation		(170)		(149)
Property and equipment, net	$	604	$	627

At December 31, 2017, the aggregate future minimum rental payments related to our non-cancellable operating leases and the capital lease were as follows (in millions):


	Capital		Operating
	lease		leases
Years ending December 31,
2018	$	72	$	15
2019		72		12
2020		72		11
2021		71		10
2022		71		10
Thereafter		479		39
Total future minimum rental payment		837	$	97
Less amount representing imputed interest		(296)
Present value of future minimum rental payments under capital leases		541
Less current portion included in debt due within one year		(30)
Long-term capital lease obligation	$	511

Purchase and service agreement obligations

We have entered into purchase obligations with shipyards and other contractors related to our newbuild construction programs. We have also entered into long‑term service agreements with original equipment manufacturers to provide services and parts related to our pressure control systems. The future payments required under our service agreements were estimated based on our projected operating activity and may vary based on actual operating activity. At December 31, 2017, the aggregate future payments required under our purchase obligations and our service agreement obligations were as follows (in millions):


			Service
	Purchase		agreement
	obligations		obligations
Years ending December 31,
2018	$	48	$	67
2019		3		100
2020		847		107
2021		—		99
2022		—		102
Thereafter		—		584
Total	$	898	$	1,059

Letters of credit and surety bonds

At December 31, 2017 and 2016, we had outstanding letters of credit totaling $29 million and $50 million, respectively, issued under various uncommitted credit lines, some of which require cash collateral, provided by several banks to guarantee various contract bidding, performance activities and customs obligations. At December 31, 2017, the aggregate cash collateral held by banks for letters of credit was $7 million. As is customary in the contract drilling business, we also have various surety bonds in place that secure customs obligations related to the importation of our rigs and certain performance and other obligations. At December 31, 2017 and 2016, we had outstanding surety bonds totaling $51 million and $33 million, respectively

Macondo well incident commitments and contingencies

Overview—On April 22, 2010, the ultra‑deepwater floater Deepwater Horizon sank after a blowout of the Macondo well caused a fire and explosion on the rig off the coast of Louisiana. At the time of the explosion, Deepwater Horizon was contracted to an affiliate of BP plc. (together with its affiliates, “BP”). Following the incident, we have been subject to civil and criminal claims, as well as causes of action, fines and penalties by local, state and federal governments. Litigation commenced shortly after the incident, and most claims against us were consolidated by the U.S. Judicial Panel on Multidistrict Litigation and transferred to the U.S. District Court for the Eastern District of Louisiana (the “MDL Court”). A significant portion of the contingencies arising from the Macondo well incident has now been resolved or is pending release of funds from escrow (see “—PSC Settlement Agreement”). As for any actions not resolved by our previous settlements, including any claims by individuals who opted out of the settlement agreement that we and the Plaintiff Steering Committee (the “PSC”) filed with the MDL Court in May 2015 (the “PSC Settlement Agreement”), we will vigorously defend those claims and pursue any and all defenses available.

In the year ended December 31, 2015, we recognized income of $788 million ($735 million, or $2.02 per diluted share, net of tax) recorded as a net reduction to operating and maintenance costs and expenses, including $538 million associated with recoveries from insurance for our previously incurred losses, $125 million associated with partial reimbursement from BP for our previously incurred legal costs, and $125 million associated with a net reduction to certain related contingent liabilities, primarily associated with contingencies that have either been settled or otherwise resolved as a result of settlements with BP and the PSC.

We have recognized a liability for the remaining estimated loss contingencies associated with litigation resulting from the Macondo well incident that we believe are probable and for which a reasonable estimate can be made. At December 31, 2017 and 2016, the liability for estimated loss contingencies that we believe are probable and for which a reasonable estimate can be made was $219 million and $250 million, respectively, recorded in other current liabilities, the majority of which is related to our settlement with the PSC.

Plea Agreement—Pursuant to the plea agreement (the “Plea Agreement”), one of our subsidiaries pled guilty to one misdemeanor count of negligently discharging oil into the U.S. Gulf of Mexico, in violation of the Clean Water Act (“CWA”) and agreed to be subject to probation through February 2018. We also agreed to make an aggregate cash payment of $400 million, including a criminal fine and cash contributions to the National Fish & Wildlife Foundation and the National Academy of Sciences, payable in scheduled installments. At December 31, 2016, the carrying amount of our liability for settlement obligations under the Plea Agreement was $60 million, recorded in other current liabilities. In the years ended December 31, 2017, 2016 and 2015, we made cash payments of $60 million in each period, representing the final installments for our obligations under the Plea Agreement.

Consent Decree—Under the civil consent decree (the “Consent Decree”), we agreed to undertake certain actions, including enhanced safety and compliance actions when operating in U.S. waters. The Consent Decree requires us to submit and make publicly available certain plans, reports and other submissions. One such plan is a performance plan, approved on January 2, 2014, that contains, among other things, interim milestones for actions in specified areas and schedules for reports required under the Consent Decree. Additionally, as required, we retained an independent auditor to review and report to the DOJ our compliance with the Consent Decree and an independent process safety consultant to review, report and assist with the process safety requirements of the Consent Decree. The Consent Decree resolved the claim by the U.S. for civil penalties under the CWA. We may request termination of the Consent Decree after January 2, 2019, provided we meet certain conditions. We also agreed to pay civil penalties of $1.0 billion plus interest. In the year ended December 31, 2015, we made a cash payment of $204 million, including interest, representing the final installment due under the Consent Decree.

PSC Settlement Agreement—On May 29, 2015, together with the PSC, we filed the PSC Settlement Agreement with the MDL Court for approval. Through the PSC Settlement Agreement, we agreed to pay a total of $212 million, plus up to $25 million for partial reimbursement of attorneys’ fees, to be allocated between two classes of plaintiffs as follows: (1) 72.8 percent to private plaintiffs, businesses, and local governments who could have asserted punitive damages claims against us under general maritime law; and (2) 27.2 percent to private plaintiffs who previously settled economic damages claims against BP and were assigned certain claims BP had made against us. In exchange for these payments, each of the classes agreed to release all respective claims it has against us. Thirty claimants elected to opt out of the PSC Settlement Agreement. In June 2016 and August 2015, we made a cash deposit of $25 million and $212 million, respectively, into escrow accounts established by the MDL Court for the settlement. On February 15, 2017, the MDL Court entered a final order and judgement approving the PSC Settlement Agreement, which is no longer subject to appeal. In November 2017, the MDL Court released $25 million from the escrow accounts for payment of attorneys’ fees. At December 31, 2017 and 2016, the aggregate balance in escrow was $212 million and $237 million, respectively, recorded in restricted cash accounts and investments.

Other legal proceedings

Asbestos litigation—In 2004, several of our subsidiaries were named, along with numerous other unaffiliated defendants, in complaints filed in the Circuit Courts of the State of Mississippi, and in 2014, a group of similar complaints were filed in Louisiana. The plaintiffs, former employees of some of the defendants, generally allege that the defendants used or manufactured asbestos containing drilling mud additives for use in connection with drilling operations, claiming negligence, products liability, strict liability and claims allowed under the Jones Act and general maritime law. The plaintiffs generally seek awards of unspecified compensatory and punitive damages, but the court appointed special master has ruled that a Jones Act employer defendant, such as us, cannot be sued for punitive damages. At December 31, 2017, eight plaintiffs have claims pending in Louisiana in which we have or may have an interest. We intend to defend these lawsuits vigorously, although we can provide no assurance as to the outcome. We historically have maintained broad liability insurance, although we are not certain whether insurance will cover the liabilities, if any, arising out of these claims. Based on our evaluation of the exposure to date, we do not expect the liability, if any, resulting from these claims to have a material adverse effect on our consolidated statement of financial position, results of operations or cash flows.

One of our subsidiaries has been named as a defendant, along with numerous other companies, in lawsuits arising out of the subsidiary’s manufacture and sale of heat exchangers, and involvement in the construction and refurbishment of major industrial complexes alleging bodily injury or personal injury as a result of exposure to asbestos. As of December 31, 2017, the subsidiary was a defendant in approximately 140 lawsuits with a corresponding number of plaintiffs. For many of these lawsuits, we have not been provided with sufficient information from the plaintiffs to determine whether all or some of the plaintiffs have claims against the subsidiary, the basis of any such claims, or the nature of their alleged injuries. The operating assets of the subsidiary were sold and its operations were discontinued in 1989, and the subsidiary has no remaining assets other than insurance policies, rights and proceeds, including (i) certain policies subject to litigation and (ii) certain rights and proceeds held directly or indirectly through a qualified settlement fund. The subsidiary has in excess of $1.0 billion in insurance limits potentially available to the subsidiary. Although not all of the policies may be fully available due to the insolvency of certain insurers, we believe that the subsidiary will have sufficient funding directly or indirectly, including from settlements and payments from insurers, assigned rights from insurers and coverage‑in‑place settlement agreements with insurers to respond to these claims. While we cannot predict or provide assurance as to the outcome of these matters, we do not expect the ultimate liability, if any, resulting from these claims to have a material adverse effect on our consolidated statement of financial position, results of operations or cash flows.

Rio de Janeiro tax assessment—In the year ended December 31, 2006, the state tax authorities of Rio de Janeiro in Brazil issued to one of our subsidiaries tax assessments on equipment imported into the state in connection with our operations, resulting from a preliminary finding by these authorities that our record keeping practices were deficient. At December 31, 2017, the aggregate tax assessment was for BRL 529 million, equivalent to approximately $160 million, including interest and penalties. In September 2006, we filed an initial response refuting these tax assessments, and, in September 2007, the state tax authorities confirmed that they believe the tax assessments are valid. On September 27, 2007, we filed an appeal with the state Taxpayer’s Council contesting the assessments. In November 2017, the Third Chamber of the Taxpayer’s Council for administrative proceedings ruled in our favor on the validity of the initial tax claims. The ruling is subject to appeal by the state tax authorities. While we cannot predict or provide assurance as to the final outcome of these proceedings, we do not expect it to have a material adverse effect on our consolidated statement of financial position, results of operations or cash flows.

Nigerian Cabotage Act litigation—In October 2007, three of our subsidiaries were each served a Notice and Demand from the Nigeria Maritime Administration and Safety Agency, imposing a two percent surcharge on the value of all contracts performed by us in Nigeria pursuant to the Coastal and Inland Shipping (Cabotage) Act 2003 (the “Cabotage Act”). Our subsidiaries each filed an originating summons in the Federal High Court in Lagos challenging the imposition of this surcharge on the basis that the Cabotage Act and associated levy is not applicable to drilling rigs. The respondents challenged the competence of the suits on several procedural grounds. The court upheld the objections and dismissed the suits. In December 2010, our subsidiaries filed a new joint Cabotage Act suit. While we cannot predict or provide assurance as to the outcome of these proceedings, we do not expect the proceedings to have a material adverse effect on our consolidated statement of financial position, results of operations or cash flows.

Global Marine litigation—On November 28, 2017, Wilmington Trust Company, in its capacity as trustee, filed a lawsuit in the Supreme Court of the State of New York, County of New York, against Global Marine Inc. (“Global Marine”), one of our wholly owned, indirect subsidiaries, seeking a declaratory judgment that Global Marine is in default under the indenture governing its $300 million of outstanding 7.00% Notes due June 2028. We disagree with the assertions in the lawsuit and believe that Global Marine is in compliance with the indenture and has meritorious defenses against these allegations, although it can make no assurance regarding the outcome of the lawsuit, including the actual amount that would be due in the event that the lawsuit is successful. The notes are neither guaranteed by, nor recourse to, Transocean Ltd. or our other subsidiaries. The claimants seek payment prior to the scheduled maturity of the principal amount of notes outstanding and accrued but unpaid interest as well as make‑whole amounts under the indenture. In addition, the acceleration of the amounts due under the indenture could, absent a waiver from the requisite lenders, result in an event of default under our currently undrawn Five‑Year Revolving Credit Facility. We intend to vigorously defend the lawsuit. While we cannot predict or provide assurance as to the outcome of these proceedings, we do not expect the proceedings to have a material adverse effect on our consolidated statement of financial position, results of operations or cash flows.

Other matters—We are involved in various tax matters, various regulatory matters, and a number of claims and lawsuits, asserted and unasserted, all of which have arisen in the ordinary course of our business. We do not expect the liability, if any, resulting from these other matters to have a material adverse effect on our consolidated statement of financial position, results of operations or cash flows. We cannot predict with certainty the outcome or effect of any of the litigation matters specifically described above or of any such other pending, threatened, or possible litigation or liability. We can provide no assurance that our beliefs or expectations as to the outcome or effect of any tax, regulatory, lawsuit or other litigation matter will prove correct and the eventual outcome of these matters could materially differ from management’s current estimates.

Other environmental matters

Hazardous waste disposal sites—We have certain potential liabilities under the Comprehensive Environmental Response, Compensation and Liability Act (“CERCLA”) and similar state acts regulating cleanup of various hazardous waste disposal sites, including those described below. CERCLA is intended to expedite the remediation of hazardous substances without regard to fault. Potentially responsible parties (“PRPs”) for each site include present and former owners and operators of, transporters to and generators of the substances at the site. Liability is strict and can be joint and several.

We have been named as a PRP in connection with a site located in Santa Fe Springs, California, known as the Waste Disposal, Inc. site. We and other PRPs have agreed with the Environmental Protection Agency (the “EPA”) and the DOJ to settle our potential liabilities for this site by agreeing to perform the remaining remediation required by the EPA. The parties to the settlement have entered into a participation agreement, which makes us liable for approximately eight percent of the remediation and related costs. The remediation is complete, and we believe our share of the future operation and maintenance costs of the site is not material. There are additional potential liabilities related to the site, but these cannot be quantified, and we have no reason at this time to believe that they will be material.

One of our subsidiaries has been ordered by the California Regional Water Quality Control Board (“CRWQCB”) to develop a testing plan for a site known as Campus 1000 Fremont in Alhambra, California, which is now a part of the San Gabriel Valley, Area 3, Superfund site. We were also advised that one or more of our subsidiaries that formerly owned and operated the site would likely be named by the EPA as PRPs. The current property owner, an unrelated party, performed the required testing and detected no contaminants. In discussions with CRWQCB staff, we were advised of their intent to issue us a “no further action” letter, but it has not yet been received. Based on the test results, we would contest any potential liability. We have no knowledge at this time of the potential cost of any remediation, who else will be named as PRPs, and whether in fact any of our subsidiaries is a responsible party. The subsidiaries in question do not own any operating assets and have limited ability to respond to any liabilities.

Resolutions of other claims by the EPA, the involved state agency or PRPs are at various stages of investigation. These investigations involve determinations of (a) the actual responsibility attributed to us and the other PRPs at the site, (b) appropriate investigatory or remedial actions and (c) allocation of the costs of such activities among the PRPs and other site users. Our ultimate financial responsibility in connection with those sites may depend on many factors, including (i) the volume and nature of material, if any, contributed to the site for which we are responsible, (ii) the number of other PRPs and their financial viability and (iii) the remediation methods and technology to be used.

It is difficult to quantify with certainty the potential cost of these environmental matters, particularly in respect of remediation obligations. Nevertheless, based upon the information currently available, we believe that our ultimate liability arising from all environmental matters, including the liability for all other related pending legal proceedings, asserted legal claims and known potential legal claims that are likely to be asserted, is adequately accrued and should not have a material effect on our consolidated statement of financial position, results of operations or cash flows.

Noncontrolling Interest

12 Months Ended

Dec. 31, 2017

Noncontrolling Interest.

Noncontrolling interest

Note 11—Noncontrolling Interest

Redeemable noncontrolling interest

Angola Deepwater Drilling Company Limited—We own a 65 percent interest and Angco Cayman Limited (“Angco Cayman”) owns a 35 percent interest, in ADDCL, a variable interest entity. Angco Cayman has the right to require us to purchase its shares for cash. Accordingly, we present the carrying amount of Angco Cayman’s ownership interest as redeemable noncontrolling interest on our consolidated balance sheets. Changes in redeemable noncontrolling interest were as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Redeemable noncontrolling interest
Balance, beginning of period	$	28	$	5	$	11
Net income (loss) attributable to noncontrolling interest		30		23		(6)
Balance, end of period	$	58	$	28	$	5

See Note 4—Variable Interest Entity.

Noncontrolling interest

Transocean Partners—Transocean Partners LLC, a Marshall Islands limited liability company and a wholly owned indirect subsidiary (“Transocean Partners”), was previously a partially owned subsidiary. In the years ended December 31, 2016 and 2015, Transocean Partners declared and paid an aggregate distribution of $99 million and $100 million, respectively, to its unitholders, of which $28 million and $29 million, respectively, was paid to the holders of noncontrolling interest. On December 9, 2016, Transocean Partners completed a merger with one of our subsidiaries as contemplated under the merger agreement. Following the completion of the merger, Transocean Partners became a wholly owned indirect subsidiary of Transocean Ltd. Each Transocean Partners common unit that was issued and outstanding immediately prior to the closing, other than the units held by Transocean and its subsidiaries, was converted into the right to receive 1.20 of our shares. To complete the merger, we issued 23.8 million shares from conditional capital.

Shareholders' Equity

12 Months Ended

Dec. 31, 2017

Shareholders' Equity

Shareholders' Equity

Note 12—Shareholders’ Equity

Par value reduction—On October 29, 2015, at our extraordinary general meeting, our shareholders approved the reduction of the par value of each of our shares to CHF 0.10 from the original par value of CHF 15.00. The reduction of par value became effective as of January 7, 2016 upon registration in the commercial register.

Distributions of qualifying additional paid‑in capital—In May 2015, at our annual general meeting, our shareholders approved the distribution of qualifying additional paid‑in capital in the form of a U.S. dollar denominated dividend of $0.60 per outstanding share, payable in four quarterly installments of $0.15 per outstanding share, subject to certain limitations. In May 2015, we recognized a liability of $218 million for the distribution payable, recorded in other current liabilities, with a corresponding entry to additional paid‑in capital. On June 17 and September 23, 2015, we paid the first two installments in the aggregate amount of $109 million to shareholders of record as of May 29 and August 25, 2015. On October 29, 2015, at our extraordinary general meeting, our shareholders approved the cancellation of the third and fourth installments of the distribution. As a result, we reduced our distribution payable, recorded in other current liabilities, by $109 million with corresponding increase to additional paid‑in capital.

In May 2014, at our annual general meeting, our shareholders approved the distribution of qualifying additional paid‑in capital in the form of a U.S. dollar denominated dividend of $3.00 per outstanding share, payable in four quarterly installments of $0.75 per outstanding share, subject to certain limitations. On March 18, 2015, we paid the final installment in the aggregate amount of $272 million to shareholders of record as of February 20, 2015.

We did not pay the distribution of qualifying additional paid‑in capital with respect to our shares held by our subsidiary or previously held in treasury.

Shares issued—To complete the merger with Transocean Partners, in December 2016, we issued 23.8 million shares from conditional capital. Each Transocean Partners common unit that was issued and outstanding immediately prior to the closing, other than the units held by Transocean and its subsidiaries, was converted into the right to receive 1.20 of our shares. See Note 1—Business, Note 11—Noncontrolling Interest, Note 15—Supplemental Cash Flow Information and Note 20—Subsequent Event.

Shares held in treasury—In May 2009, at our annual general meeting, our shareholders approved and authorized our board of directors, at its discretion, to repurchase an amount of our shares for cancellation with an aggregate purchase price of up to CHF 3.5 billion. On February 12, 2010, our board of directors authorized our management to implement the share repurchase program. During the three‑year period ended December 31, 2017, we did not purchase any shares under our share repurchase program. At December 31, 2015, we held 2.9 million shares in treasury, recorded at cost. On October 29, 2015, at our extraordinary general meeting, our shareholders approved the cancellation of the 2.9 million shares previously purchased under the share repurchase program and held in treasury, and such cancellation became effective as of January 7, 2016 upon registration in the commercial register.

Shares held by subsidiaries—Two of our subsidiaries hold our shares for future use to satisfy our obligations to deliver shares in connection with awards granted under our incentive plans or other rights to acquire our shares. At December 31, 2017 and 2016, our subsidiaries held 3.6 million shares and 5.4 million shares, respectively.

Accumulated other comprehensive loss—The changes in accumulated other comprehensive loss, presented net of tax, for our defined benefit pension plans were as follows (in millions):


	Years ended December 31,
	2017		2016

Balance, beginning of period	$	(283)	$	(277)
Other comprehensive loss before reclassifications		(2)		(15)
Reclassifications to net income		(5)		9
Other comprehensive loss, net		(7)		(6)
Balance, end of period	$	(290)	$	(283)

Share-Based Compensation

12 Months Ended

Dec. 31, 2017

Share-Based Compensation

Share-Based Compensation

Note 13—Share‑Based Compensation

Overview

We have a long‑term incentive plan (the “Long‑Term Incentive Plan”) for executives, key employees and non‑employee directors under which awards can be granted in the form of restricted share units, restricted shares, stock options, stock appreciation rights and cash performance awards. Awards may be granted as service awards that are earned over a defined service period or as performance awards that are earned based on the achievement of certain market factors or performance targets or a combination of market factors and performance targets. Our compensation committee of our board of directors determines the terms and conditions of the awards granted under the Long‑Term Incentive Plan. As of December 31, 2017, under the current plan established in 2015, we had 20.7 million shares authorized and 9.9 million shares available to be granted under the Long‑Term Incentive Plan. As of December 31, 2017, total unrecognized compensation costs related to all unvested share‑based awards were $43 million, which are expected to be recognized over a weighted average period of 1.7 years.

Service awards typically vest either in three equal annual installments beginning on the first anniversary date of the grant or in an aggregate installment at the end of the stated vesting period. Performance awards typically are subject to a three-year measurement period during which the number of options or shares to be issued remains uncertain. At the end of the measurement period, the awarded number of options or shares to be issued is determined. The performance awards typically vest in one aggregate installment following the determination date. Stock options and stock appreciation rights are subject to a stated vesting period and, once vested, typically have a seven‑year term during which they are exercisable.

Service awards

Restricted share units—A restricted share unit is a notional unit that is equal to one share but has no voting rights until the underlying share is issued. The following table summarizes unvested activity for service‑based units granted under our incentive plans during the year ended December 31, 2017:


	Number	Weighted-average
	of	grant-date fair value
	units	per unit
Unvested at January 1, 2017	4,006,082	$	13.10
Granted	1,921,029		13.03
Vested	(1,867,970)		15.14
Forfeited	(238,686)		11.42
Unvested at December 31, 2017	3,820,455	$	12.15

During the year ended December 31, 2017, the aggregate grant‑date fair value of the service‑based units that vested was $28 million. During the years ended December 31, 2016 and 2015, we granted 3,155,382 and 2,848,521 service‑based units, respectively, with a weighted‑average grant‑date fair value of $8.69 and $18.70 per unit, respectively. During the years ended December 31, 2016 and 2015, we had 1,725,734 and 1,817,758 service‑based units, respectively, that vested with an aggregate grant‑date fair value of $48 million and $81 million, respectively.

Stock options—During the years ended December 31, 2017 and 2016, we granted service‑based stock options. The following table summarizes activity for vested and unvested service‑based stock options outstanding under our incentive plans during the year ended December 31, 2017:


				Weighted-average
	Number	Weighted-average		remaining	Aggregate
	of shares	exercise price		contractual term	intrinsic value
	under option	per share		(years)	(in millions)
Outstanding at January 1, 2017	1,934,695	$	44.88	6.12	$	6
Granted	877,231
Forfeited	(58,463)
Outstanding at December 31, 2017	2,753,463	$	34.98	6.37	$	2

Vested and exercisable at December 31, 2017	1,263,702	$	62.78	3.63	$	—

During the year ended December 31, 2017, the weighted‑average grant‑date fair value of the service‑based stock options that we granted was $6.46 per option. During the year ended December 31, 2017, the aggregate grant‑date fair value of service‑based stock options that vested was $2 million. During the year ended December 31, 2017, no service‑based stock options were exercised. As of December 31, 2017, there were outstanding unvested service‑based stock options to purchase 1,489,761 shares. During the year ended December 31, 2016, we granted service‑based stock options to purchase 945,724 shares with a weighted‑average grant‑date fair value of $5.11 per option. During the year ended December 31, 2015, we did not grant service‑based stock options. During the year ended December 31, 2016 and 2015, the aggregate grant‑date fair value of service‑based options that vested was $3 million and $9 million, respectively. During the years ended December 31, 2016 and 2015, no service‑based stock options were exercised.

Performance awards

Restricted share units—We grant performance awards in the form of restricted share units that can be earned depending on the achievement of (a) market factors or (b) both market factors and performance targets. The number of shares ultimately earned per unit is quantified upon completion of the specified period at the determination date. The following table summarizes unvested activity for performance‑based units under our incentive plans during the year ended December 31, 2017:


	Number	Weighted-average
	of	grant-date fair value
	units	per unit
Unvested at January 1, 2017	1,439,606	$	14.40
Granted	689,740		16.25
Vested	(478,492)		13.87
Forfeited	(12,173)		11.60
Unvested at December 31, 2017	1,638,681	$	13.56

During the year ended December 31, 2017, performance‑based units vested with an aggregate grant‑date fair value of $7 million. During the years ended December 31, 2016 and 2015, we granted 997,362 and 652,592 performance‑based units, respectively, with a weighted‑average grant‑date fair value of $11.60 and $17.91 per unit, respectively. During the year ended December 31, 2016, the total grant‑date fair value of the performance‑based units that vested was $6 million. During the year ended December 31, 2015, no performance‑based units vested since neither the market factors nor the performance targets were achieved.

Supplemental Balance Sheet Information

12 Months Ended

Dec. 31, 2017

Supplemental Balance Sheet Information

Supplemental Balance Sheet Information

Note 14—Supplemental Balance Sheet Information

Other current liabilities were comprised of the following (in millions):


	December 31,
	2017		2016
Other current liabilities
Accrued payroll and employee benefits	$	176	$	200
Accrued interest		127		135
Accrued taxes, other than income		67		87
Macondo well incident settlement obligations		—		60
Deferred revenues		213		209
Contingent liabilities		246		262
Other		10		7
Total other current liabilities	$	839	$	960

Other long‑term liabilities were comprised of the following (in millions):


	December 31,
	2017		2016
Other long-term liabilities
Postemployment benefit plan obligations	$	353	$	370
Income taxes payable		247		333
Deferred revenues		422		390
Other		60		60
Total other long-term liabilities	$	1,082	$	1,153

Supplemental Cash Flow Information

12 Months Ended

Dec. 31, 2017

Supplemental Cash Flow Information

Supplemental Cash Flow Information

Note 15—Supplemental Cash Flow Information

Net cash provided by operating activities attributable to the net change in other operating assets and liabilities was comprised of the following (in millions):


	Years ended December 31,
	2017		2016		2015
Changes in operating assets and liabilities
Decrease in accounts receivable	$	230	$	350	$	742
Increase in other current assets		(30)		(29)		(177)
(Increase) decrease in other assets		(33)		(12)		5
Decrease in accounts payable and other current liabilities		(115)		(286)		(828)
Decrease in other long-term liabilities		(13)		(55)		(72)
Change in income taxes receivable / payable, net		(58)		(133)		(65)
	$	(19)	$	(165)	$	(395)

Additional cash flow information was as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Certain cash operating activities
Cash payments for interest	$	486	$	351	$	439
Cash payments for income taxes		124		172		314

Non-cash investing and financing activities
Capital additions, accrued at end of period (a)	$	20	$	42	$	128
Issuance of shares to acquire noncontrolling interest (b)		—		317		—

(a)

Additions to property and equipment for which we had accrued a corresponding liability in accounts payable at the end of the period. See Note 5—Drilling Fleet.

(b)

On December 9, 2016, we issued 23.8 million shares in connection with our acquisition of the outstanding publicly held common units of Transocean Partners pursuant to its merger with one of our other subsidiaries. See Note 11—Noncontrolling Interest and Note 12—Shareholders’ Equity.

Financial Instruments

12 Months Ended

Dec. 31, 2017

Financial Instruments

Financial Instruments

Note 16—Financial Instruments

The carrying amounts and fair values of our financial instruments were as follows (in millions):


	December 31, 2017				December 31, 2016
	Carrying		Fair		Carrying		Fair
	amount		value		amount		value
Cash and cash equivalents	$	2,519	$	2,519	$	3,052	$	3,052
Short-term investments		450		450		—		—
Restricted cash accounts and investments		489		489		510		511
Long-term debt, including current maturities		7,396		7,538		8,464		8,218

We estimated the fair value of each class of financial instruments, for which estimating fair value is practicable, by applying the following methods and assumptions:

Cash and cash equivalents—The carrying amount of cash and cash equivalents represents the historical cost, plus accrued interest. Our cash equivalents are primarily invested in short‑term time deposits and money market funds. The carrying amount of our cash and cash equivalents approximates fair value because of the short maturities of the instruments. At December 31, 2017 and 2016, the aggregate carrying amount of our cash equivalents was $2.1 billion and $2.6 billion, respectively.

Short‑term investments—The carrying amount of unrestricted short‑term investments represents the historical cost of the time deposits in which they are invested. The carrying amount of such short‑term investments approximates fair value because of the short maturities of the instruments.

Restricted cash accounts and investments—The carrying amount of the cash and cash equivalents that are subject to restrictions due to collateral requirements, legislation, regulation or court order approximates fair value due to the short term nature of the instruments in which the restricted cash balances are held. At December 31, 2017, the aggregate carrying amount of such restricted cash and cash equivalents was $456 million, including $440 million and $16 million recorded in current assets and other assets, respectively. At December 31, 2016, the aggregate carrying amount of such restricted cash and cash equivalents was $387 million, including $368 million and $19 million recorded in current assets and other assets, respectively.

The carrying amount of the restricted cash investments pledged for debt service of the Eksportfinans Loans due January 2018 and for security of certain other credit arrangements represents the amortized historical cost of the investment. We measured the estimated fair value of such restricted cash investments using significant other observable inputs, representative of a Level 2 fair value measurement, including the terms and credit spreads of the instruments. At December 31, 2017 and 2016, the aggregate carrying amount of the restricted cash investments was $33 million and $123 million, respectively. At December 31, 2017 and 2016, the estimated fair value of such restricted cash investments was $33 million and $124 million, respectively.

Debt—We measured the estimated fair value of our debt, all of which was fixed‑rate debt, using significant other observable inputs, representative of a Level 2 fair value measurement, including the terms and credit spreads for the instruments.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Risk Concentration	12 Months Ended
Risk Concentration	Dec. 31, 2017
Risk Concentration
Risk Concentration	Note 17—Risk Concentration Interest rate risk—Financial instruments that potentially subject us to concentrations of interest rate risk include our cash equivalents, short‑term investments, restricted cash investments, debt and capital lease obligations. We are exposed to interest rate risk related to our cash equivalents and short‑term investments, as the interest income earned on these investments, is based on variable or short‑term interest rates, which change with market interest rates. We are also exposed to the interest rate risk related to our fixed‑rate debt when we refinance maturing debt with new debt or when we repurchase debt in open market repurchases. Currency exchange rate risk—Our international operations expose us to currency exchange rate risk. This risk is primarily associated with compensation costs of our employees and purchasing costs from non‑U.S. suppliers, which are denominated in currencies other than the U.S. dollar. We use a variety of techniques to minimize the exposure to currency exchange rate risk, including the structuring of customer contract payment terms. Our primary currency exchange rate risk management strategy involves structuring customer contracts to provide for payment in both U.S. dollars and local currency. The payment portion denominated in local currency is based on anticipated local currency requirements over the contract term. Due to various factors, including customer acceptance, local banking laws, national content requirements, other statutory requirements, local currency convertibility and the impact of inflation on local costs, actual local currency needs may vary from those anticipated in the customer contracts, resulting in partial exposure to currency exchange rate risk. The currency exchange effect resulting from our international operations generally has not had a material impact on our operating results. Credit risk—Financial instruments that potentially subject us to concentrations of credit risk are primarily cash and cash equivalents, short‑term investments and trade receivables, both current and long‑term. We generally maintain our cash, cash equivalents and short‑term investments in time deposits at commercial banks with high credit ratings or mutual funds, which invest exclusively in high‑quality money market instruments. We limit the amount of exposure to any one institution and do not believe we are exposed to any significant credit risk. We earn our revenues by providing our drilling services to international oil companies, government‑owned oil companies and government‑controlled oil companies. Receivables are dispersed in various countries (see Note 18—Operating Segments, Geographic Analysis and Major Customers). We establish an allowance for doubtful accounts on a case‑by‑case basis, considering changes in the financial position of a customer, when we believe the required payment of specific amounts owed to us is unlikely to occur. Although we have encountered only isolated credit concerns related to independent oil companies, we occasionally require collateral or other security to support customer receivables. In certain instances, when we determine that collection is not reasonably assured, we may occasionally offer extended payment terms and recognize revenues associated with the contract on a cash basis. Labor agreements—We require highly skilled personnel to operate our drilling units. We conduct extensive personnel recruiting, training and safety programs. At December 31, 2017, we had approximately 4,900 employees, including approximately 400 persons engaged through contract labor providers. Approximately 26 percent of our total workforce, working primarily in Brazil, Norway and the U.K. are represented by, and some of our contracted labor work is subject to, collective bargaining agreements, substantially all of which are subject to annual salary negotiation. These negotiations could result in higher personnel expenses, other increased costs or increased operational restrictions as the outcome of such negotiations affect the market for all offshore employees not just the union members.

Operating Segments, Geographic Analysis and Major Customers

12 Months Ended

Dec. 31, 2017

Operating Segments, Geographic Analysis and Major Customers

Operating Segments, Geographic Analysis and Major Customers

Note 18—Operating Segments, Geographic Analysis and Major Customers

Operating segments—We operate in a single, global market for the provision of contract drilling services to our customers. The location of our rigs and the allocation of our resources to build or upgrade rigs are determined by the activities and needs of our customers.

Geographic analysis—Operating revenues by country were as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Operating revenues
U.S.	$	1,527	$	1,977	$	2,416
Brazil		335		453		673
U.K.		288		551		1,139
Other countries (a)		823		1,180		3,158
Total operating revenues	$	2,973	$	4,161	$	7,386

(a)

Other countries represent countries in which we operate that individually had operating revenues representing less than 10 percent of consolidated operating revenues earned.

Long‑lived assets by country were as follows (in millions):


	December 31,
	2017		2016
Long-lived assets
U.S.	$	7,541	$	6,181
Trinidad		2,563		3,977
Other countries (a)		7,298		10,935
Total long-lived assets	$	17,402	$	21,093

(a)

Other countries represents countries in which we operate that individually had long‑lived assets representing less than 10 percent of consolidated long‑lived assets.

Since the majority of our assets are mobile, the geographic locations of such assets at the end of the periods are not necessarily indicative of the geographic distribution of the operating revenues generated by such assets during the periods. Although we are organized under the laws of Switzerland, we do not conduct any operations and do not have operating revenues in Switzerland. At December 31, 2017 and 2016, the aggregate carrying amount of our long‑lived assets located in Switzerland was less than $1 million and $2 million, respectively.

Our international operations are subject to certain political and other uncertainties, including risks of war and civil disturbances or other market disrupting events, expropriation of equipment, repatriation of income or capital, taxation policies, and the general hazards associated with certain areas in which we operate.

Major customers—For the year ended December 31, 2017, Chevron Corporation (together with its affiliates, “Chevron”), Royal Dutch Shell plc (together with its affiliates, “Shell”) and Petróleo Brasileiro S.A. (“Petrobras”) accounted for approximately 29 percent, 17 percent and 14 percent, respectively, of our consolidated operating revenues. For the year ended December 31, 2016, Chevron, BP, Shell and Petrobras accounted for approximately 24 percent, 12 percent, 12 percent and 11 percent, respectively, of our consolidated operating revenues from continuing operations. For the year ended December 31, 2015, Chevron and Shell accounted for approximately 14 percent and 10 percent of our consolidated operating revenues.

Quarterly Results (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Results (Unaudited)

Quarterly Results (Unaudited)

Note 19—Quarterly Results (Unaudited)


	Three months ended
	March 31,		June 30,		September 30,		December 31,
	(In millions, except per share data)
2017
Operating revenues	$	785	$	751	$	808	$	629
Operating income (loss) (a)		173		(1,544)		(1,145)		12
Income (loss) from continuing operations (a)		95		(1,679)		(1,411)		(102)
Net income (loss) (a)		95		(1,679)		(1,411)		(102)
Net income (loss) attributable to controlling interest (a)		91		(1,690)		(1,417)		(111)
Per share earnings (loss) from continuing operations
Basic	$	0.23	$	(4.32)	$	(3.62)	$	(0.28)
Diluted	$	0.23	$	(4.32)	$	(3.62)	$	(0.28)
Weighted-average shares outstanding
Basic		390		391		391		391
Diluted		390		391		391		391

2016
Operating revenues	$	1,341	$	940	$	906	$	974
Operating income (b)		424		163		229		316
Income from continuing operations (b)		242		92		236		257
Net income (b)		241		93		236		257
Net income attributable to controlling interest (b)		235		82		218		243
Per share earnings from continuing operations
Basic	$	0.64	$	0.22	$	0.59	$	0.64
Diluted	$	0.64	$	0.22	$	0.59	$	0.64
Weighted-average shares outstanding
Basic		364		365		365		371
Diluted		364		365		365		371

(a)

Second quarter and third quarter included an aggregate loss of $1.4 billion associated with the impairment of certain drilling units classified as assets held for sale. Second quarter included a loss of $94 million associated with the impairment of our midwater floater asset group. Second quarter included a loss of $1.6 billion associated with the sale of 10 high‑specification jackups and the novation of five high‑specification jackups under construction. First quarter, second quarter, third quarter and fourth quarter included an aggregate loss of $55 million associated with the retirement of debt.

(b)

First quarter, second quarter, third quarter and fourth quarter included an aggregate loss $41 million associated with the impairment of certain drilling units classified as assets held for sale. Fourth quarter included a loss of $52 million associated with the impairment of our deepwater asset group. Fourth quarter included income of $30 million associated with recoveries of previously incurred costs associated with the Macondo well incident. Second quarter and third quarter included a gain of $38 million and $110 million, respectively, associated with the retirement of debt. See Note 5—Drilling Fleet, Note 8—Debt and Note 10—Commitments and Contingencies.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2017
Subsequent Events
Subsequent Events	Note 20—Subsequent Event Business combination—On August 13, 2017, we entered into the Transaction Agreement with Songa pursuant to which we agreed to offer to acquire all of the issued and outstanding shares of Songa through the Offer in exchange for consideration per Songa share, consisting of (i) 0.3572 newly issued shares of Transocean Ltd. and (ii) approximately $2.99726 principal amount of 0.5% Exchangeable Senior Bonds due January 2023 (the “Exchangeable Bonds”) to be issued by Transocean Inc., our wholly owned direct subsidiary and a Cayman Islands exempted company. Additionally, each Songa shareholder could elect to receive a cash payment of NOK 47.50 per Songa share up to a maximum of NOK 125,000 per shareholder in lieu of some or all of the consideration such shareholder would otherwise be entitled to receive in the Offer. We believe the acquisition of Songa strengthens and solidifies our position as a leader in harsh environment and ultra‑deepwater drilling services by adding significant high value assets, including four high‑specification harsh environment floaters, supported by significant contract backlog. Additionally, the acquisition strengthens our footprint in harsh environment operating areas and our existing relationship with Statoil ASA. In connection with the acquisition, shareholders at our extraordinary general meeting, on January 16, 2018, were requested to consider the following: (1) the issuance of up to 68.6 million Transocean Ltd. shares, (2) an amendment of our articles of association to create additional authorized share capital, (3) election of one new director to our board of directors and (4) issuance of consideration shares of our authorized share capital and our shares issuable upon exchange of the Exchangeable Bonds. On January 18, 2018, we announced that shareholders at our extraordinary general meeting approved all proposals related to the Songa acquisition. On January 30, 2018, we completed the acquisition of an approximate 97.7 percent ownership interest in Songa, and we issued 66.9 million shares with an aggregate market value of $735 million, equivalent to $10.99 per share, estimated based on the market value of our shares on the date of issuance to shareholders of Songa as partial consideration for the acquired Songa shares. Additionally, we made an aggregate cash payment of less than $1 million to Songa shareholders that elected to receive a cash payment. We also issued an aggregate principal amount of $854 million of the Exchangeable Bonds as partial consideration for the acquisition of the acquired Songa shares and partial settlement of certain Songa indebtedness. Transocean Inc. is the issuer of the Exchangeable Bonds, which are fully and unconditionally guaranteed by Transocean Ltd. and rank equally with our other senior unsecured debt. We will pay interest on the Exchangeable Bonds semiannually, commencing July 30, 2018. Holders of the Exchangeable Bonds may convert the notes into shares of Transocean Ltd. under certain circumstances at a rate of 97.29756 shares per $1,000 note, equivalent to a conversion price of $10.28 per share, subject to adjustment due to the occurrence of certain events. By March 31, 2018, we expect to complete the acquisition of the remaining shares not owned by us through a compulsory acquisition, which is available to us under Cyprus law. In connection with the compulsory acquisition, we expect to issue 1.6 million shares and an aggregate principal amount of $13 million of the Exchangeable Bonds as consideration for the remaining Songa shares. We have not completed our preliminary allocation of the acquisition price to the assets acquired and liabilities assumed given the timing of the acquisition date, on January 30, 2018, relative to the date of issuance of our financial statements as of and for the year ended December 31, 2017.

Schedule II - Valuation and Qualifying Accounts

12 Months Ended

Dec. 31, 2017

Schedule II - Valuation and Qualifying Accounts

Schedule II - Valuation and Qualifying Accounts

Transocean Ltd. and Subsidiaries

Schedule II ‑ Valuation and Qualifying Accounts

(In millions)


			Additions
					Charge to
	Balance at		Charge to cost		other					Balance at
	beginning of		and		accounts		Deductions			end of
	period		expenses		-describe		-describe			period

Year ended December 31, 2015
Reserves and allowances deducted from asset accounts:
Allowance for doubtful accounts receivable	$	14	$	—	$	—	$	14	(a)	$	—
Allowance for obsolete materials and supplies		109		62		—		23	(b)		148
Valuation allowance on deferred tax assets		409		10		—		39	(c)		380

Year ended December 31, 2016
Reserves and allowances deducted from asset accounts:
Allowance for doubtful accounts receivable	$	—	$	—	$	—	$	—		$	—
Allowance for obsolete materials and supplies		148		15		—		10	(b)		153
Valuation allowance on deferred tax assets		380		32		—		—			412

Year ended December 31, 2017
Reserves and allowances deducted from asset accounts:
Allowance for doubtful accounts receivable	$	—	$	—	$	—	$	—		$	—
Allowance for obsolete materials and supplies		153		24		—		36	(b)		141
Valuation allowance on deferred tax assets		412		162		—		—			574

(a)

Uncollectible accounts receivable written off, net of recoveries.

(b)

Amount related to materials and supplies on rigs and related equipment sold or classified as held for sale.

Amount related to deferred tax asset recorded for net operating losses with an offsetting valuation allowance.

Significant Accounting Policies (Policies)	12 Months Ended
Significant Accounting Policies (Policies)	Dec. 31, 2017
Significant Accounting Policies
Accounting estimates	Accounting estimates—To prepare financial statements in accordance with accounting principles generally accepted in the United States (“U.S.”), we are required to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosures of contingent assets and liabilities. On an ongoing basis, we evaluate our estimates and assumptions, including those related to our allowance for doubtful accounts, materials and supplies obsolescence, property and equipment, assets held for sale, income taxes, contingencies, share‑based compensation, defined benefit pension and other postemployment benefit plans. We base our estimates and assumptions on historical experience and on various other factors we believe are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying amounts of assets and liabilities that are not readily apparent from other sources. Actual results could differ from such estimates.
Fair value measurements	Fair value measurements—We estimate fair value at a price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants in the principal market for the asset or liability. Our valuation techniques require inputs that we categorize using a three‑level hierarchy, from highest to lowest level of observable inputs, as follows: (1) significant observable inputs, including unadjusted quoted prices for identical assets or liabilities in active markets (“Level 1”), (2) significant other observable inputs, including direct or indirect market data for similar assets or liabilities in active markets or identical assets or liabilities in less active markets (“Level 2”) and (3) significant unobservable inputs, including those that require considerable judgment for which there is little or no market data (“Level 3”). When multiple input levels are required for a valuation, we categorize the entire fair value measurement according to the lowest level of input that is significant to the measurement even though we may have also utilized significant inputs that are more readily observable.
Consolidation	Consolidation—We consolidate entities in which we have a majority voting interest and entities that meet the criteria for variable interest entities for which we are deemed to be the primary beneficiary for accounting purposes. We eliminate intercompany transactions and accounts in consolidation. We apply the equity method of accounting for an investment in an entity if we have the ability to exercise significant influence over the entity that (a) does not meet the variable interest entity criteria or (b) meets the variable interest entity criteria, but for which we are not deemed to be the primary beneficiary. We apply the cost method of accounting for an investment in an entity if we do not have the ability to exercise significant influence over the unconsolidated entity. We separately present within equity on our consolidated balance sheets the ownership interests attributable to parties with noncontrolling interests in our consolidated subsidiaries, and we separately present net income attributable to such parties on our consolidated statements of operations. See Note 4—Variable Interest Entities and Note 11—Noncontrolling Interest.
Business combination	Business combination—In connection with our acquisition of Songa, we will apply the acquisition method of accounting. Accordingly, we will record the acquired assets and assumed liabilities at fair value and recognize goodwill to the extent the fair value of the business acquired exceeds the fair value of the net assets. We will estimate the fair values of the acquired assets and assumed liabilities as of the date of the acquisition, and our estimates will be subject to adjustment based on our final assessments of the fair values of property and equipment, intangible assets, liabilities and our evaluation of tax positions and contingencies. We will complete our final assessments of the fair values of the acquired assets and assumed liabilities and our final evaluations of uncertain tax positions and contingencies within one year of the acquisition date. See Note 20—Subsequent Event.
Operating revenues and expenses	Operating revenues and expenses—We recognize operating revenues as they are realized and earned and can be reasonably measured, based on contractual dayrates, and when collectability is reasonably assured. In certain instances, when we determine that collection is not reasonably assured, we recognize revenues associated with the contract when all revenue recognition criteria have been met. In connection with drilling contracts, we may receive revenues for preparation and mobilization of equipment and personnel or for capital improvements to rigs. We defer the revenues earned and incremental costs incurred that are directly related to contract preparation and mobilization and recognize such revenues and costs over the primary contract term of the drilling project using the straight‑line method. We recognize, in operating and maintenance costs and expenses, the fees related to contract preparation and mobilization on a straight‑line basis over the estimated firm period of drilling, which is consistent with the general pace of activity, level of services being provided and dayrates being earned over the life of the contract. For contractual daily rate contracts, we recognize the losses for loss contracts as such losses are incurred. We recognize the costs of relocating drilling units without contracts to more promising market sectors as such costs are incurred. Upon completion of drilling contracts, we recognize in earnings any demobilization fees received and expenses incurred. We defer capital upgrade revenues received and recognize such revenues over the primary contract term of the drilling project. We depreciate the actual costs incurred for the capital upgrade on a straight‑line basis over the estimated useful life of the asset. We defer the periodic survey and drydock costs incurred in connection with obtaining regulatory certification to operate our rigs and well control systems on an ongoing basis, and we recognize such costs over the period until the next survey using the straight-line method. See Note 3—Accounting Standards Updates.
Other revenues	Our other revenues represent those derived from customer contract terminations and customer reimbursable items. We recognize revenues from contract terminations as we fulfill our obligations for such terminations and when all contingencies have expired. We recognize customer reimbursable revenues as we bill our customers for reimbursement of costs associated with certain equipment, materials and supplies, subcontracted services, employee bonuses and other expenditures, resulting in little or no net effect on operating income since such recognition is concurrent with the recognition of the respective reimbursable costs in operating and maintenance expense.
Share-based compensation	Share‑based compensation—To measure the fair values of stock options and stock appreciation rights granted or modified, we use the Black‑Scholes‑Merton option‑pricing model and apply assumptions for the expected life, risk‑free interest rate, dividend yield and expected volatility. To measure the fair values of granted or modified service‑based restricted share units, we use the market price of our shares on the grant date or modification date. To measure the fair values of restricted share units that are subject to performance targets, we use the market price of our shares on the measurement date for the projected number of shares expected to be earned at the end of the performance period. To measure the fair values of granted or modified restricted share units that are subject to market factors, we use a Monte Carlo simulation model and, in addition to the assumptions applied for the Black‑Scholes‑Merton option‑pricing model, we apply assumptions using a risk neutral approach and an average price at the performance start date. We recognize share‑based compensation expense in the same financial statement line item as cash compensation paid to the respective employees or non‑employee directors. For service awards, we recognize compensation expense on a straight‑line basis over the service period through the date the employee or non‑employee director is no longer required to provide service to earn the award. For performance awards with graded vesting conditions, we recognize compensation expense on a straight‑line basis over the service period for each separately vesting portion of the award as if the award was, in substance, multiple awards. In the years ended December 31, 2017, 2016 and 2015, share‑based compensation expense was $41 million, $42 million and $64 million, respectively. See Note 13—Share Based Compensation Plans.
Capitalized interest	Capitalized interest—We capitalize interest costs for qualifying construction and upgrade projects and only capitalize interest costs during periods in which progress for the construction projects continues to be underway. As of December 31, 2017, we had ceased capitalization of interest costs on one uncontracted newbuild drillship due to a pause in construction in progress. In the years ended December 31, 2017, 2016 and 2015, we capitalized interest costs of $116 million, $176 million and $140 million, respectively, for our construction work in progress.
Functional currency	Functional currency—We consider the U.S. dollar to be the functional currency for all of our operations since the majority of our revenues and expenditures are denominated in U.S. dollars, which limits our exposure to currency exchange rate fluctuations. We recognize currency exchange rate gains and losses in other, net. In the years ended December 31, 2017, 2016 and 2015, we recognized a net loss of $6 million, a net loss of $2 million and a net gain of less than $1 million, respectively, related to currency exchange rates.
Income taxes	Income taxes—We provide for income taxes based upon the tax laws and rates in effect in the countries in which operations are conducted and income is earned. We recognize the effect of changes in tax laws as of the date of enactment. There is little or no expected relationship between the provision for or benefit from income taxes and income or loss before income taxes because the countries in which we operate have taxation regimes that vary not only with respect to nominal rate, but also in terms of the availability of deductions, credits and other benefits. Variations also arise because income earned and taxed in any particular country or countries may fluctuate from year to year. We measure deferred tax assets and liabilities using enacted tax rates that will apply in the years in which the temporary differences are expected to be recovered or paid. We record a valuation allowance for deferred tax assets when it is more likely than not that some or all of the benefit from the deferred tax asset will not be realized. In evaluating our ability to realize deferred tax assets, we consider all available positive and negative evidence, including projected future taxable income and the existence of cumulative losses in recent years. We also record a valuation allowance for deferred tax assets resulting from net operating losses incurred during the year in certain jurisdictions and for other deferred tax assets where, in our opinion, it is more likely than not that the financial statement benefit of these losses will not be realized. Additionally, we record a valuation allowance for foreign tax credit carryforwards to reflect the possible expiration of these benefits prior to their utilization. We maintain liabilities for estimated tax exposures in our jurisdictions of operation, and we recognize the provisions and benefits resulting from changes to those liabilities in our income tax expense or benefit along with related interest and penalties. Tax exposure items include potential challenges to permanent establishment positions, intercompany pricing, disposition transactions, and withholding tax rates and their applicability. These tax exposures are resolved primarily through the settlement of audits within these tax jurisdictions or by judicial means, but can also be affected by changes in applicable tax law or other factors, which could cause us to revise past estimates. See Note 6—Income Taxes.
Cash and cash equivalents	Cash and cash equivalents—We consider cash equivalents to include highly liquid debt instruments with original maturities of three months or less such as time deposits with commercial banks that have high credit ratings, U.S. Treasury and government securities, Eurodollar time deposits, certificates of deposit and commercial paper. We may also invest excess funds in no‑load, open‑ended, management investment trusts. Such management trusts invest exclusively in high‑quality money market instruments.
Short-term investments	Short‑term investments—We periodically deposit unrestricted excess funds in time deposits and commercial paper with original maturities beyond three months. Such short‑term investments are with commercial banks and companies with high credit ratings. At December 31, 2017, the carrying amount of our short‑term investments was $450 million.
Accounts receivable	Accounts receivable—We earn our revenues by providing our drilling services to international oil companies and government‑owned or government‑controlled oil companies. We evaluate the credit quality of our customers on an ongoing basis, and we may occasionally require collateral or other security to support customer receivables. We establish an allowance for doubtful accounts on a case‑by‑case basis, considering changes in the financial position of a customer, when we believe the required payment of specific amounts owed to us is unlikely to occur. At December 31, 2017 and 2016, the allowance for doubtful accounts was less than $1 million.
Materials and supplies	Materials and supplies—We record materials and supplies at their average cost less an allowance for obsolescence. We estimate the allowance for obsolescence based on historical experience and expectations for future use of the materials and supplies. At December 31, 2017 and 2016, the allowance for obsolescence was $141 million and $153 million, respectively.
Restricted cash accounts and investments	Restricted cash accounts and investments—We maintain restricted cash balances and investments that are either pledged for debt service under certain bond indentures, as required under certain bank credit arrangements, or held in accounts that are subject to restrictions due to legislation, regulation or court order. We classify such restricted cash investment balances in current assets if the restriction is expected to expire or otherwise be resolved within one year and in other assets if the restriction is expected to expire or otherwise be resolved in greater than one year. At December 31, 2017, the aggregate carrying amount of our restricted cash investments was $489 million, of which $466 million and $23 million was classified in current assets and other assets, respectively. At December 31, 2016, the aggregate carrying amount of our restricted cash investments was $510 million, of which $466 million and $44 million was classified in current assets and other assets, respectively. See Note 3—Accounting Standards Updates, Note 8—Debt and Note 10—Commitments and Contingencies.
Assets held for sale	Assets held for sale—We classify an asset as held for sale when the facts and circumstances meet the criteria for such classification, including the following: (a) we have committed to a plan to sell the asset, (b) the asset is available for immediate sale, (c) we have initiated actions to complete the sale, including locating a buyer, (d) the sale is expected to be completed within one year, (e) the asset is being actively marketed at a price that is reasonable relative to its fair value, and (f) the plan to sell is unlikely to be subject to significant changes or termination. At December 31, 2017 and 2016, the aggregate carrying amount of our assets held for sale, recorded in other current assets, was $22 million and $6 million, respectively. See Note 5—Drilling Fleet.
Property and equipment	Property and equipment—The carrying amounts of our property and equipment, consisting primarily of offshore drilling rigs and related equipment, are based on our estimates, assumptions and judgments relative to capitalized costs, useful lives and salvage values of our rigs. These estimates, assumptions and judgments reflect both historical experience and expectations regarding future industry conditions and operations. At December 31, 2017, the aggregate carrying amount of our property and equipment represented approximately 78 percent of our total assets. We capitalize expenditures for newbuilds, renewals, replacements and improvements, including capitalized interest, if applicable, and we recognize the expense for maintenance and repair costs as incurred. For newbuild construction projects, we also capitalize the initial preparation, mobilization and commissioning costs incurred until the drilling unit is placed into service. Upon sale or other disposition of an asset, we recognize a net gain or loss on disposal of the asset, which is measured as the difference between the net carrying amount of the asset and the net proceeds received. We compute depreciation using the straight‑line method after allowing for salvage values. The estimated original useful lives of our drilling units range from 25 to 35 years, our buildings and improvements range from two to 30 years and our machinery and equipment range from four to 20 years. We reevaluate the remaining useful lives and salvage values of our rigs when certain events occur that directly impact the useful lives and salvage values of the rigs, including changes in operating condition, functional capability and market and economic factors. When evaluating the remaining useful lives of rigs, we also consider major capital upgrades required to perform certain contracts and the long‑term impact of those upgrades on future marketability.
Long lived asset impairment	Long‑lived asset impairment—We review the carrying amounts of long‑lived assets, principally property and equipment, for potential impairment when events occur or circumstances change that indicate that the carrying amount of such assets may not be recoverable. For assets classified as held and used, we determine recoverability by evaluating the estimated undiscounted future net cash flows based on projected dayrates and utilization of the asset group under review. We consider our asset groups to be ultra‑deepwater floaters, harsh environment floaters, deepwater floaters and midwater floaters. When an impairment of one or more of our asset groups is indicated, we measure the impairment as the amount by which the asset group’s carrying amount exceeds its estimated fair value. We measure the fair values of our contract drilling asset groups by applying a variety of valuation methods, incorporating a combination of cost, income and market approaches, using projected discounted cash flows and estimates of the exchange price that would be received for the assets in the principal or most advantageous market for the assets in an orderly transaction between market participants as of the measurement date. For an asset classified as held for sale, we consider the asset to be impaired to the extent its carrying amount exceeds its estimated fair value less cost to sell. In the year ended December 31, 2017, we determined that the carrying amount of the midwater floater asset group exceeded its fair value, and we recognized a loss of $94 million ($93 million, or $0.25 per diluted share, net of tax) associated with the impairment of these long‑lived assets. In the year ended December 31, 2016, we determined that the carrying amount of the deepwater floater asset group exceeded its fair value, and we recognized a loss of $52 million ($0.14 per diluted share), which had no tax effect, associated with the impairment of these long‑lived assets. In the year ended December 31, 2015, we determined that the carrying amount of the deepwater floater asset group and the midwater floater asset group each exceeded its fair value, and we recognized a loss of $507 million ($481 million, or $1.31 per diluted share, net of tax) and $668 million ($654 million, or $1.78 per diluted share, net of tax) associated with the impairment of the deepwater floater asset group and the midwater floater asset group, respectively, including a loss of $52 million associated with construction in progress related to the asset groups. If we experience increasingly unfavorable changes to actual or anticipated dayrates or other impairment indicators, or if we are unable to secure new or extended contracts for our active units or the reactivation of any of our stacked units, we may be required to recognize additional losses in future periods as a result of impairments of the carrying amount of one or more of our asset groups. See Note 5—Drilling Fleet.
Pension and other postretirement benefits	Pension and other postemployment benefit plans—We use a measurement date of January 1 for determining net periodic benefit costs and December 31 for determining plan benefit obligations and the fair values of plan assets. We determine our net periodic benefit costs based on a market‑related value of assets that reduces year‑to‑year volatility by including investment gains or losses subject to amortization over a five‑year period from the year in which they occur. Investment gains or losses for this purpose are measured as the difference between the expected return calculated using the market‑related value of assets and the actual return based on the market‑related value of assets. If gains or losses exceed 10 percent of the greater of plan assets or plan liabilities, we amortize such gains or losses over the average expected future service period of the employee participants. We measure our actuarially determined obligations and related costs for our defined benefit pension and other postemployment benefit plans, retiree life insurance and medical benefits, by applying assumptions, including long‑term rate of return on plan assets, discount rates, mortality rates and employee turnover rates. For our defined benefit plans that have ceased accruing benefits, certain assumptions, including compensation increases and health care cost trend rates no longer apply. The two most critical assumptions are the long‑term rate of return on plan assets and the discount rate. For the long‑term rate of return, we develop our assumptions regarding the expected rate of return on plan assets based on historical experience and projected long‑term investment returns, and we weight the assumptions based on each plan’s asset allocation. For the discount rate, we base our assumptions on a yield curve approach using Aa‑rated corporate bonds and the expected timing of future benefit payments. For the projected compensation trend rate, we consider short‑term and long‑term compensation expectations for participants, including salary increases and performance bonus payments. At December 31, 2017 and 2016, our pension and other postemployment benefit plan obligations represented an aggregate liability of $359 million and $375 million, respectively, and an aggregate asset of $17 million and $5 million, respectively, representing the funded status of the plans. In the years ended December 31, 2017, 2016 and 2015, aggregate net periodic benefit costs were costs of $5 million, income of $11 million and costs of $26 million, respectively. See Note 3—Accounting Standards Updates and Note 9—Postemployment Benefit Plans.
Contingencies	Contingencies—We perform assessments of our contingencies on an ongoing basis to evaluate the appropriateness of our liabilities and disclosures for such contingencies. We establish liabilities for estimated loss contingencies when we believe a loss is probable and the amount of the probable loss can be reasonably estimated. We recognize corresponding assets for those loss contingencies that we believe are probable of being recovered through insurance. Once established, we adjust the carrying amount of a contingent liability upon the occurrence of a recognizable event when facts and circumstances change, altering our previous assumptions with respect to the likelihood or amount of loss. We recognize expense for legal costs as they are incurred, and we recognize a corresponding asset for such legal costs only if we expect such legal costs to be recovered through insurance.
Reclassifications	Reclassifications—We have made certain reclassifications to prior period amounts to conform with the current year’s presentation. Such reclassifications did not have a material effect on our consolidated statement of financial position, results of operations or cash flows.

Variable Interest Entities (Tables)

12 Months Ended

Dec. 31, 2017

Variable Interest Entities

Carrying Amounts of Variable Interest Entities

The carrying amounts associated with ADDCL, after eliminating the effect of intercompany transactions, was as follows (in millions):


	Years ended December 31,
	2017		2016
Assets	$	716	$	787
Liabilities		7		25
Net carrying amount	$	709	$	762

- Definition

Tabular disclosure of the significant judgments and assumptions made in determining whether a variable interest (as defined) held by the entity requires the variable interest entity (VIE) (as defined) to be consolidated and (or) disclose information about its involvement with the VIE, individually or in aggregate (as applicable); the nature of restrictions, if any, on the consolidated VIE's assets and on the settlement of its liabilities reported by an entity in its statement of financial position, including the carrying amounts of such assets and liabilities; the nature of, and changes in, the risks associated with involvement in the VIE; how involvement with the VIE affects the entity's financial position, financial performance, and cash flows; the lack of recourse if creditors (or beneficial interest holders) of the consolidated VIE have no recourse to the general credit of the primary beneficiary (if applicable); the terms of arrangements, giving consideration to both explicit arrangements and implicit variable interests, if any, that could require the entity to provide financial support to the VIE, including events or circumstances that could expose the entity to a loss; the methodology used by the entity for determining whether or not it is the primary beneficiary of the variable interest entity; the significant factors considered and judgments made in determining that the power to direct the activities of a VIE that most significantly impact the VIE's economic performance are shared (as defined); the carrying amounts and classification of assets and liabilities of the VIE included in the statement of financial position; the entity's maximum exposure to loss, if any, as a result of its involvement with the VIE, including how the maximum exposure is determined and significant sources of the entity's exposure to the VIE; a comparison of the carrying amounts of the assets and liabilities and the entity's maximum exposure to loss; information about any liquidity arrangements, guarantees, and (or) other commitments by third parties that may affect the fair value or risk of the entity's variable interest in the VIE; whether or not the entity has provided financial support or other support (explicitly or implicitly) to the VIE that it was not previously contractually required to provide or whether the entity intends to provide that support, including the type and amount of the support and the primary reasons for providing the support; and supplemental information the entity determines necessary to provide.

+ References + Details

Drilling Fleet (Tables)

12 Months Ended

Dec. 31, 2017

Drilling Fleet

Changes in our construction work in progress, including capital expenditures and capitalized interest

For each of the three years in the period ended December 31, 2017, the changes in our construction work in progress, including capital expenditures and other capital additions, were as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Construction work in progress, at beginning of period	$	2,171	$	3,735	$	2,447

Capital expenditures
Newbuild construction program		397		1,206		1,622
Other equipment and construction projects		100		138		379
Total capital expenditures		497		1,344		2,001
Changes in accrued capital additions		(23)		(86)		(11)
Impairment of construction work in progress		—		—		(52)

Construction work in progress sold		(289)		—		—
Property and equipment placed into service
Newbuild construction program		(896)		(2,557)		—
Other property and equipment		(68)		(265)		(650)
Construction work in progress, at end of period	$	1,392	$	2,171	$	3,735

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Taxes

Components of the provision (benefit) for income taxes

The components of our provision (benefit) for income taxes were as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Current tax expense	$	5	$	39	$	254
Deferred tax expense (benefit)		89		68		(134)
Income tax expense	$	94	$	107	$	120

Reconciliation of the differences between income tax expense computed at the Swiss holding company statutory rate and the reported provision for income taxes


	Years ended December 31,
	2017		2016		2015

Income tax expense (benefit)	$	(235)	$	72	$	80
Impairment losses subject to rates different than the Swiss federal statutory rate		241		5		(8)
Change in valuation allowance		162		32		10
Impact of U.S. tax reform		66		—		—
Revaluation of Norwegian assets		1		18		14
Litigation matters, primarily related to the Macondo well incident		(70)		(1)		(9)
Changes in unrecognized tax benefits, net		(56)		(31)		12
Benefit from foreign tax credits		(15)		(16)		(10)
Earnings subject to rates different than the Swiss federal statutory rate		2		34		36
Other, net		(2)		(6)		(5)
Income tax expense	$	94	$	107	$	120

Significant components of deferred tax assets and liabilities

The significant components of our deferred tax assets and liabilities were as follows (in millions):


	December 31,
	2017		2016
Deferred tax assets
Net operating loss carryforwards	$	435	$	383
Deferred income		101		122
Accrued payroll expenses not currently deductible		54		110
Loss contingencies		42		68
Tax credit carryforwards		37		33
United Kingdom charter limitation		36		33
Professional fees		3		3
Other		30		37
Valuation allowance		(574)		(412)
Total deferred tax assets		164		377

Deferred tax liabilities
Depreciation and amortization		(157)		(239)
Other		(4)		(18)
Total deferred tax liabilities		(161)		(257)

Net deferred tax assets	$	3	$	120

Reconciliation of unrecognized tax benefits, excluding interest and penalties

The changes to our liabilities related to unrecognized tax benefits, excluding interest and penalties that we recognize as a component of income tax expense, were as follows (in millions):


	Years ended December 31,
		2017		2016		2015
Balance, beginning of period	$	274	$	287	$	272
Additions for prior year tax positions		17		13		17
Additions for current year tax positions		13		42		36
Reductions for prior year tax positions		(68)		(34)		(27)
Reductions related to statute of limitation expirations		(13)		(15)		(6)
Reductions due to settlements		(1)		(19)		(5)
Balance, end of period	$	222	$	274	$	287

Schedule of unrecognized tax benefits, including related interest and penalties

The liabilities related to our unrecognized tax benefits, including related interest and penalties that we recognize as a component of income tax expense, were as follows (in millions):


	December 31,
		2017		2016
Unrecognized tax benefits, excluding interest and penalties	$	222	$	274
Interest and penalties		87		96
Unrecognized tax benefits, including interest and penalties	$	309	$	370

Earnings (Loss) Per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings (Loss) Per Share

Earnings (Loss) Per Share

The numerator and denominator used for the computation of basic and diluted per share earnings from continuing operations were as follows (in millions, except per share data):


	Years ended December 31,
	2017				2016				2015
	Basic		Diluted		Basic		Diluted		Basic		Diluted
Numerator for earnings (loss) per share
Income (loss) from continuing operations attributable to controlling interest	$	(3,127)	$	(3,127)	$	778	$	778	$	865	$	865
Undistributed earnings allocable to participating securities		—		—		(14)		(14)		(8)		(8)
Income (loss) from continuing operations available to shareholders	$	(3,127)	$	(3,127)	$	764	$	764	$	857	$	857

Denominator for earnings (loss) per share
Weighted-average shares outstanding		391		391		367		367		363		363
Effect of stock options and other share-based awards		—		—		—		—		—		—
Weighted-average shares for per share calculation		391		391		367		367		363		363

Per share earnings (loss) from continuing operations	$	(8.00)	$	(8.00)	$	2.08	$	2.08	$	2.36	$	2.36

Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt

Debt, net of unamortized discounts, premiums and fair value adjustments

The aggregate principal amounts and aggregate carrying amounts, net of debt‑related balances, including unamortized discounts, premiums, issue costs and fair value adjustments, of our debt were as follows (in millions):


	Principal amount				Carrying amount
	December 31,		December 31,		December 31,		December 31,
	2017		2016		2017		2016
2.50% Senior Notes due October 2017 (a)	$	—	$	485	$	—	$	484
Eksportfinans Loans due January 2018		26		123		26		123
6.00% Senior Notes due March 2018 (a)		—		754		—		757
7.375% Senior Notes due April 2018 (a)		—		211		—		211
6.50% Senior Notes due November 2020 (a)		286		508		288		513
6.375% Senior Notes due December 2021 (a)		328		552		327		549
5.52% Senior Secured Notes due May 2022 (b)		362		—		356		—
3.80% Senior Notes due October 2022 (a)		506		539		502		534
9.00% Senior Notes due July 2023 (c)		1,250		1,250		1,216		1,211
7.75% Senior Secured Notes due October 2024 (d)		540		600		526		583
6.25% Senior Secured Notes due December 2024 (d)		562		625		549		609
7.50% Senior Notes due January 2026 (c)		750		—		742		—
7.45% Notes due April 2027 (a)		88		88		86		86
8.00% Debentures due April 2027 (a)		57		57		57		57
7.00% Notes due June 2028		300		300		307		308
Capital lease contract due August 2029		541		566		541		566
7.50% Notes due April 2031 (a)		588		588		585		585
6.80% Senior Notes due March 2038 (a)		1,000		1,000		991		991
7.35% Senior Notes due December 2041 (a)		300		300		297		297
Total debt		7,484		8,546		7,396		8,464
Less debt due within one year
2.50% Senior Notes due October 2017 (a)		—		485		—		484
Eksportfinans Loans due January 2018		26		98		26		98
5.52% Senior Secured Notes due May 2022 (b)		79		—		77		—
7.75% Senior Secured Notes due October 2024 (b)		60		60		57		57
6.25% Senior Secured Notes due December 2024 (b)		62		63		60		60
Capital lease contract due August 2029		30		25		30		25
Total debt due within one year		257		731		250		724
Total long-term debt	$	7,227	$	7,815	$	7,146	$	7,740

(a)

(b)

(c)

Scheduled maturities of debt

Scheduled maturities—At December 31, 2017, the scheduled maturities of our debt were as follows (in millions):


	Total
Years ending December 31,
2018	$	257
2019		237
2020		531
2021		580
2022		687
Thereafter		5,192
Total principal amount of debt		7,484
Total debt-related balances, net		(88)
Total carrying amount of debt	$	7,396

Schedule of tender offers



	Years ended
	December 31,
	2017			2016

2.50% Senior Notes due October 2017	$	271	$	—
6.00% Senior Notes due March 2018		400		—
7.375% Senior Notes due April 2018		128		—
6.50% Senior Notes due November 2020		207		348
6.375% Senior Notes due December 2021		213		476
3.80% Senior Notes due October 2022		—		157
Aggregate principal amount retired	$	1,219	$	981

Aggregate cash payment	$	1,269	$	876
Aggregate net gain (loss)	$	(48)	$	104

Schedule of debt repurchases and redemptions

During the years ended December 31, 2017, 2016 and 2015, we repurchased in the open market or redeemed debt securities with aggregate principal amounts as follows (in millions):


	Years ended December 31,
		2017		2016		2015

4.95% Senior Notes due November 2015	$	—	$	—	$	893
5.05% Senior Notes due December 2016		—		36		25
2.50% Senior Notes due October 2017		62		85		180
6.00% Senior Notes due March 2018		354		35		211
7.375% Senior Notes due April 2018		83		26		10
6.50% Senior Notes due November 2020		15		44		—
6.375% Senior Notes due December 2021		10		122		50
3.80% Senior Notes due October 2022		33		38		16
7.45% Notes due April 2027		—		8		4
7.50% Notes due April 2031		—		5		7
Aggregate principal amount retired	$	557	$	399	$	1,396

Aggregate cash payment	$	564	$	354	$	1,372
Aggregate net gain (loss)	$	(7)	$	44	$	23

Postemployment Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2017

Postemployment Benefit Plans

Schedule of weighted-average assumptions used to estimate benefit obligations


	December 31, 2017						December 31, 2016
	U.S.		Non-U.S.		OPEB		U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Plans		Plans		Plans
Discount rate	3.68	%	2.49	%	2.93	%	4.26	%	2.69	%	3.08	%
Compensation trend rate	na		2.50	%	na		na		2.25	%	na

Schedule of weighted-average assumptions used to estimate net periodic benefit costs


	Year ended December 31, 2017						Year ended December 31, 2016						Year ended December 31, 2015
	U.S.		Non-U.S.		OPEB		U.S.		Non-U.S.		OPEB		U.S.		Non-U.S.
	Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans		OPEB Plans
Discount rate	4.26	%	2.69	%	3.08	%	4.56	%	3.69	%	3.13	%	4.16	%	3.26	%	3.86	%
Expected rate of return	6.31	%	4.79	%	na		6.82	%	5.85	%	na		7.79	%	5.93	%	na
Compensation trend rate	na	%	2.25	%	na		0.22	%	4.01	%	na		0.21	%	3.83	%	na
Health care cost trend rate
-initial	na		na		na		na		na		na		na		na		7.81	%
-ultimate	na		na		na		na		na		na		na		na		5.00	%
-ultimate year	na		na		na		na		na		na		na		na		2023

“na” means not applicable.

Schedule of changes in projected benefit obligation, plan assets and funded status and the amounts recognized on consolidated balance sheets

The changes in projected benefit obligation, plan assets and funded status and the amounts recognized on our consolidated balance sheets were as follows (in millions):


	Year ended December 31, 2017								Year ended December 31, 2016
	U.S.		Non-U.S.		OPEB				U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total		Plans		Plans		Plans		Total
Change in projected benefit obligation
Projected benefit obligation, beginning of period	$	1,557	$	398	$	19	$	1,974	$	1,523	$	502	$	24	$	2,049
Actuarial (gains) losses, net		115		18		2		135		52		36		(3)		85
Service cost		3		3		—		6		3		10		—		13
Interest cost		65		11		—		76		69		17		1		87
Currency exchange rate changes		—		35		—		35		—		(77)		—		(77)
Participant contributions		—		—		—		—		—		—		1		1
Benefits paid		(60)		(86)		(2)		(148)		(90)		(46)		(4)		(140)
Settlements and curtailments		—		—		—		—		—		(44)		—		(44)
Projected benefit obligation, end of period		1,680		379		19		2,078		1,557		398		19		1,974

Change in plan assets
Fair value of plan assets, beginning of period		1,204		400		—		1,604		1,198		439		—		1,637
Actual return on plan assets		198		31		—		229		93		84		—		177
Currency exchange rate changes		—		36		—		36		—		(80)		—		(80)
Employer contributions		1		12		2		15		3		43		3		49
Participant contributions		—		—		—		—		—		—		1		1
Benefits paid		(60)		(86)		(2)		(148)		(90)		(46)		(4)		(140)
Settlements		—		—		—		—		—		(40)		—		(40)
Fair value of plan assets, end of period		1,343		393		—		1,736		1,204		400		—		1,604

Funded status, end of period	$	(337)	$	14	$	(19)	$	(342)	$	(353)	$	2	$	(19)	$	(370)

Balance sheet classification, end of period:
Pension asset, non-current	$	—	$	17	$	—	$	17	$	—	$	5	$	—	$	5
Pension liability, current		(2)		(1)		(3)		(6)		(2)		—		(3)		(5)
Pension liability, non-current		(335)		(2)		(16)		(353)		(351)		(3)		(16)		(370)
Accumulated other comprehensive income (loss) (a)		(301)		(84)		19		(366)		(316)		(94)		23		(387)

(a)

Amounts are before income tax effect.

Schedule of aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets

The aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets were as follows (in millions):


	December 31, 2017								December 31, 2016
	U.S.		Non-U.S.		OPEB				U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total		Plans		Plans		Plans		Total
Projected benefit obligation	$	1,680	$	5	$	19	$	1,704	$	1,557	$	5	$	19	$	1,581
Fair value of plan assets		1,343		2		—		1,345		1,204		2		—		1,206

Schedule of aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets

The aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets were as follows (in millions):


	December 31, 2017								December 31, 2016
	U.S.		Non-U.S.		OPEB				U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total		Plans		Plans		Plans		Total
Accumulated benefit obligation	$	1,680	$	3	$	19	$	1,702	$	1,557	$	4	$	19	$	1,580
Fair value of plan assets		1,343		—		—		1,343		1,204		—		—		1,204

Schedule of weighted average target and actual allocations of the investments of Transocean benefit plans


	December 31, 2017									December 31, 2016
		Target allocation				Actual allocation				Target allocation				Actual allocation
		U.S.		Non-U.S.		U.S.		Non-U.S.		U.S.		Non-U.S.		U.S.		Non-U.S.
		Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans
Equity securities		50	%	39	%	52	%	39	%	50	%	45	%	53	%	45	%
Fixed income securities		50	%	50	%	48	%	48	%	50	%	45	%	47	%	44	%
Other investments		—		11	%	—		13	%	—		10	%	—	%	11	%
Total		100	%	100	%	100	%	100	%	100	%	100	%	100	%	100	%

Schedule of fair value of the assets of Transocean benefit plans by asset category and their level within the fair value hierarchy

As of December 31, 2017, the investments for our funded Transocean Plans were categorized as follows (in millions):


	December 31, 2017
	Significant observable inputs						Significant other observable inputs						Total
	U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean
	Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans
Mutual funds
U.S. equity funds	$	557	$	—	$	557	$	—	$	—	$	—	$	557	$	—	$	557
Non-U.S. equity funds		138		—		138		5		153		158		143		153		296
Bond funds		629		—		629		8		190		198		637		190		827
Total mutual funds		1,324		—		1,324		13		343		356		1,337		343		1,680

Other investments
Cash and money market funds		6		7		13		—		—		—		6		7		13
Property collective trusts		—		—		—		—		20		20		—		20		20
Investment contracts		—		—		—		—		23		23		—		23		23
Total other investments		6		7		13		—		43		43		6		50		56

Total investments	$	1,330	$	7	$	1,337	$	13	$	386	$	399	$	1,343	$	393	$	1,736

As of December 31, 2016, the investments for our funded Transocean Plans were categorized as follows (in millions):


	December 31, 2016
	Significant observable inputs						Significant other observable inputs						Total
	U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean
	Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans
Mutual funds
U.S. equity funds	$	516	$	—	$	516	$	2	$	—	$	2	$	518	$	—	$	518
Non-U.S. equity funds		113		—		113		4		181		185		117		181		298
Bond funds		567		—		567		—		178		178		567		178		745
Total mutual funds		1,196		—		1,196		6		359		365		1,202		359		1,561

Other investments
Cash and money market funds		2		2		4		—		—		—		2		2		4
Property collective trusts		—		—		—		—		17		17		—		17		17
Investment contracts		—		—		—		—		22		22		—		22		22
Total other investments		2		2		4		—		39		39		2		41		43

Total investments	$	1,198	$	2	$	1,200	$	6	$	398	$	404	$	1,204	$	400	$	1,604

Schedule of Net Periodic Benefit Costs Before Tax

Net periodic benefit costs, before tax, included the following components (in millions):


	Year ended December 31, 2017						Year ended December 31, 2016						Year ended December 31, 2015
	U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean		U.S.		Non-U.S.		Transocean
	Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans		Plans
Net periodic benefit costs
Service cost	$	3	$	3	$	6	$	3	$	10	$	13	$	5	$	26	$	31
Interest cost		65		11		76		69		17		86		65		19		84
Expected return on plan assets		(74)		(20)		(94)		(80)		(25)		(105)		(87)		(28)		(115)
Settlements and curtailments		—		13		13		—		(5)		(5)		3		2		5
Actuarial (gain) loss, net		5		1		6		5		(1)		4		11		11		22
Prior service cost, net		—		—		—		—		—		—		—		—		—
Net periodic benefit costs	$	(1)	$	8	$	7	$	(3)	$	(4)	$	(7)	$	(3)	$	30	$	27

Schedule of amounts in accumulated other comprehensive income, before tax, that have not been recognized as components of net periodic benefit costs

The following table presents the amounts in accumulated other comprehensive income (loss), before tax, that have not been recognized as components of net periodic benefit costs (in millions):


	December 31, 2017								December 31, 2016
	U.S.		Non-U.S.		OPEB				U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total		Plans		Plans		Plans		Total
Actuarial gain (loss), net	$	(301)	$	(84)	$	(4)	$	(389)	$	(316)	$	(94)	$	(3)	$	(413)
Prior service cost, net		—		—		23		23		—		—		26		26
Total	$	(301)	$	(84)	$	19	$	(366)	$	(316)	$	(94)	$	23	$	(387)

Schedule of amounts in accumulated other comprehensive income expected to be recognized as components of net periodic benefit costs in next fiscal year


	Year ending December 31, 2018
	U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total
Actuarial loss, net	$	7	$	1	$	1	$	9
Prior service cost, net		—		—		(3)		(3)
Total amount expected to be recognized	$	7	$	1	$	(2)	$	6

Schedule of projected benefits payments

The following were the projected benefits payments (in millions):


	U.S.		Non-U.S.		OPEB
	Plans		Plans		Plans		Total
Years ending December 31,
2018	$	71	$	8	$	3	$	82
2019		73		7		3		83
2020		75		8		3		86
2021		79		8		2		89
2022		80		9		2		91
2023 - 2027		421		60		7		488

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies

Schedule of capital leased assets

At December 31, 2017 and 2016, the aggregate carrying amount of this asset held under capital lease was as follows (in millions):


	December 31,
		2017	2016
Property and equipment, cost	$	774	$	776
Accumulated depreciation		(170)		(149)
Property and equipment, net	$	604	$	627

Schedule of aggregate future minimum rental payments related to noncancellable operating leases and the capital leases

At December 31, 2017, the aggregate future minimum rental payments related to our non-cancellable operating leases and the capital lease were as follows (in millions):


	Capital		Operating
	lease		leases
Years ending December 31,
2018	$	72	$	15
2019		72		12
2020		72		11
2021		71		10
2022		71		10
Thereafter		479		39
Total future minimum rental payment		837	$	97
Less amount representing imputed interest		(296)
Present value of future minimum rental payments under capital leases		541
Less current portion included in debt due within one year		(30)
Long-term capital lease obligation	$	511

Schedule of aggregate future payments required under purchase obligations


			Service
	Purchase		agreement
	obligations		obligations
Years ending December 31,
2018	$	48	$	67
2019		3		100
2020		847		107
2021		—		99
2022		—		102
Thereafter		—		584
Total	$	898	$	1,059

Noncontrolling Interest (Tables)

12 Months Ended

Dec. 31, 2017

Noncontrolling Interest.

Changes in redeemable noncontrolling interest


	Years ended December 31,
	2017		2016		2015
Redeemable noncontrolling interest
Balance, beginning of period	$	28	$	5	$	11
Net income (loss) attributable to noncontrolling interest		30		23		(6)
Balance, end of period	$	58	$	28	$	5

Shareholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Shareholders' Equity

Changes in accumulated other comprehensive loss

The changes in accumulated other comprehensive loss, presented net of tax, for our defined benefit pension plans were as follows (in millions):


	Years ended December 31,
	2017		2016

Balance, beginning of period	$	(283)	$	(277)
Other comprehensive loss before reclassifications		(2)		(15)
Reclassifications to net income		(5)		9
Other comprehensive loss, net		(7)		(6)
Balance, end of period	$	(290)	$	(283)

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Share Based Compensation

Summary of activity for vested and unvested stock options outstanding


				Weighted-average
	Number	Weighted-average		remaining	Aggregate
	of shares	exercise price		contractual term	intrinsic value
	under option	per share		(years)	(in millions)
Outstanding at January 1, 2017	1,934,695	$	44.88	6.12	$	6
Granted	877,231
Forfeited	(58,463)
Outstanding at December 31, 2017	2,753,463	$	34.98	6.37	$	2

Vested and exercisable at December 31, 2017	1,263,702	$	62.78	3.63	$	—

Time-based awards

Share Based Compensation

Summary of unvested deferred units activity


	Number	Weighted-average
	of	grant-date fair value
	units	per unit
Unvested at January 1, 2017	4,006,082	$	13.10
Granted	1,921,029		13.03
Vested	(1,867,970)		15.14
Forfeited	(238,686)		11.42
Unvested at December 31, 2017	3,820,455	$	12.15

Performance-based awards

Share Based Compensation

Summary of unvested deferred units activity


	Number	Weighted-average
	of	grant-date fair value
	units	per unit
Unvested at January 1, 2017	1,439,606	$	14.40
Granted	689,740		16.25
Vested	(478,492)		13.87
Forfeited	(12,173)		11.60
Unvested at December 31, 2017	1,638,681	$	13.56

Supplemental Balance Sheet Information (Tables)

12 Months Ended

Dec. 31, 2017

Supplemental Balance Sheet Information

Schedule of other current liabilities

Other current liabilities were comprised of the following (in millions):


	December 31,
	2017		2016
Other current liabilities
Accrued payroll and employee benefits	$	176	$	200
Accrued interest		127		135
Accrued taxes, other than income		67		87
Macondo well incident settlement obligations		—		60
Deferred revenues		213		209
Contingent liabilities		246		262
Other		10		7
Total other current liabilities	$	839	$	960

Schedule of other long term liabilities

Other long‑term liabilities were comprised of the following (in millions):


	December 31,
	2017		2016
Other long-term liabilities
Postemployment benefit plan obligations	$	353	$	370
Income taxes payable		247		333
Deferred revenues		422		390
Other		60		60
Total other long-term liabilities	$	1,082	$	1,153

Supplemental Cash Flow Information (Tables)

12 Months Ended

Dec. 31, 2017

Supplemental Cash Flow Information

Schedule of changes in operating assets and liabilities

Net cash provided by operating activities attributable to the net change in other operating assets and liabilities was comprised of the following (in millions):


	Years ended December 31,
	2017		2016		2015
Changes in operating assets and liabilities
Decrease in accounts receivable	$	230	$	350	$	742
Increase in other current assets		(30)		(29)		(177)
(Increase) decrease in other assets		(33)		(12)		5
Decrease in accounts payable and other current liabilities		(115)		(286)		(828)
Decrease in other long-term liabilities		(13)		(55)		(72)
Change in income taxes receivable / payable, net		(58)		(133)		(65)
	$	(19)	$	(165)	$	(395)

Additional cash flow information


	Years ended December 31,
	2017		2016		2015
Changes in operating assets and liabilities
Decrease in accounts receivable	$	230	$	350	$	742
Increase in other current assets		(30)		(29)		(177)
(Increase) decrease in other assets		(33)		(12)		5
Decrease in accounts payable and other current liabilities		(115)		(286)		(828)
Decrease in other long-term liabilities		(13)		(55)		(72)
Change in income taxes receivable / payable, net		(58)		(133)		(65)
	$	(19)	$	(165)	$	(395)

Additional cash flow information was as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Certain cash operating activities
Cash payments for interest	$	486	$	351	$	439
Cash payments for income taxes		124		172		314

Non-cash investing and financing activities
Capital additions, accrued at end of period (a)	$	20	$	42	$	128
Issuance of shares to acquire noncontrolling interest (b)		—		317		—

(a)

Additions to property and equipment for which we had accrued a corresponding liability in accounts payable at the end of the period. See Note 5—Drilling Fleet.

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Financial Instruments

Carrying amounts and fair values of the financial instruments


	December 31, 2017				December 31, 2016
	Carrying		Fair		Carrying		Fair
	amount		value		amount		value
Cash and cash equivalents	$	2,519	$	2,519	$	3,052	$	3,052
Short-term investments		450		450		—		—
Restricted cash accounts and investments		489		489		510		511
Long-term debt, including current maturities		7,396		7,538		8,464		8,218

Operating Segments, Geographic Analysis and Major Customers (Tables)

12 Months Ended

Dec. 31, 2017

Operating Segments, Geographic Analysis and Major Customers

Schedule of operating revenues for continuing operations by country

Operating revenues by country were as follows (in millions):


	Years ended December 31,
	2017		2016		2015
Operating revenues
U.S.	$	1,527	$	1,977	$	2,416
Brazil		335		453		673
U.K.		288		551		1,139
Other countries (a)		823		1,180		3,158
Total operating revenues	$	2,973	$	4,161	$	7,386

(a)

Other countries represent countries in which we operate that individually had operating revenues representing less than 10 percent of consolidated operating revenues earned.

Schedule of long-lived assets of the entity's continuing operations by country

Long‑lived assets by country were as follows (in millions):


	December 31,
	2017		2016
Long-lived assets
U.S.	$	7,541	$	6,181
Trinidad		2,563		3,977
Other countries (a)		7,298		10,935
Total long-lived assets	$	17,402	$	21,093

(a)

Other countries represents countries in which we operate that individually had long‑lived assets representing less than 10 percent of consolidated long‑lived assets.

Quarterly Results (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Results (Unaudited)

Schedule of Quarterly Financial Data (Unaudited)


	Three months ended
	March 31,		June 30,		September 30,		December 31,
	(In millions, except per share data)
2017
Operating revenues	$	785	$	751	$	808	$	629
Operating income (loss) (a)		173		(1,544)		(1,145)		12
Income (loss) from continuing operations (a)		95		(1,679)		(1,411)		(102)
Net income (loss) (a)		95		(1,679)		(1,411)		(102)
Net income (loss) attributable to controlling interest (a)		91		(1,690)		(1,417)		(111)
Per share earnings (loss) from continuing operations
Basic	$	0.23	$	(4.32)	$	(3.62)	$	(0.28)
Diluted	$	0.23	$	(4.32)	$	(3.62)	$	(0.28)
Weighted-average shares outstanding
Basic		390		391		391		391
Diluted		390		391		391		391

2016
Operating revenues	$	1,341	$	940	$	906	$	974
Operating income (b)		424		163		229		316
Income from continuing operations (b)		242		92		236		257
Net income (b)		241		93		236		257
Net income attributable to controlling interest (b)		235		82		218		243
Per share earnings from continuing operations
Basic	$	0.64	$	0.22	$	0.59	$	0.64
Diluted	$	0.64	$	0.22	$	0.59	$	0.64
Weighted-average shares outstanding
Basic		364		365		365		371
Diluted		364		365		365		371

(a)

Business (Details) - item		12 Months Ended
Business (Details) - item	May 31, 2017	Dec. 31, 2017	Jun. 30, 2017
Songa
Number of mobile offshore drilling units		7
Number of Harsh Environment Floaters		5
Number of Midwater Floaters (in drilling units)		2
Continuing operations
Number of mobile offshore drilling units		39
Number of Ultra-Deepwater Floaters		26
Number of Harsh Environment Floaters		7
Number of Deepwater Floaters		2
Number of Midwater Floaters (in drilling units)		4
Number of Ultra-Deepwater drillships under construction (in drilling units)		3
Sale of high specification jackups \| Assets sold, not discontinued operations
Number of high specification jackups operated through contract completion or novation	3	2
Number of High-Specification Jackups (in drilling units)	10		10
Number of High-Specification Jackup under construction (in drilling units)	5		5

Significant Accounting Policies (Details) $ in Millions	12 Months Ended
Significant Accounting Policies (Details) $ in Millions	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Share-based compensation expense
Share-based compensation expense	$ 41	$ 42	$ 64
Capitalized interest
Number of newbuilds ceased to capitalize interest \| item	1
Capitalized interest costs on construction work in progress	$ 116	176	140
Functional currency
Net foreign currency exchange gain (loss)	(6)	(2)
Restricted cash accounts and investments
Restricted cash investments	489	510
Restricted cash investments classified as current	466	466
Restricted cash investments classified in other assets	23	44
Materials and supplies
Materials and supplies, allowance for obsolescence	141	153
Short term investments
Short-term Investments	450
Assets held for sale
Assets held for sale, included in other current assets	$ 22	6
Property and equipment
Property and equipment as a percentage of total assets	78.00%
Maximum
Functional currency
Net foreign currency exchange gain (loss)			$ 1
Accounts receivable
Allowance for doubtful accounts	$ 1	$ 1
Drilling rig units \| Minimum
Property and equipment
Estimated original useful life	25 years
Drilling rig units \| Maximum
Property and equipment
Estimated original useful life	35 years
Buildings and improvements \| Minimum
Property and equipment
Estimated original useful life	2 years
Buildings and improvements \| Maximum
Property and equipment
Estimated original useful life	30 years
Machinery and equipment \| Minimum
Property and equipment
Estimated original useful life	4 years
Machinery and equipment \| Maximum
Property and equipment
Estimated original useful life	20 years

Significant Accounting Policies (Impair and Pensions) (Details) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) item $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares
Pension and other postretirement benefits
Recognition period of investment gains or losses related to asset valuation for determining net periodic benefit cost			5 years
Conditional amortization gains or losses as percentage of greater of plan assets or liabilities, minimum			10.00%
Number of critical fair value assumptions \| item			2
Pension liability, current and noncurrent		$ 375	$ 359	$ 375
Pension asset, non-current		5	17	5
Net periodic benefit costs			5	(11)	$ 26
Construction in Progress
Long-Live assets
Loss associated with impairment					52
Deepwater Floater asset group
Long-Live assets
Loss associated with impairment		$ 52		$ 52	507
Loss associated with impairment, net of tax					$ 481
Loss associated with impairment per diluted share \| $ / shares				$ 0.14	$ 1.31
Loss associated with impairment, tax effect				$ 0
Midwater Floater asset group
Long-Live assets
Loss associated with impairment	$ 94		94		$ 668
Loss associated with impairment, net of tax			$ 93		$ 654
Loss associated with impairment per diluted share \| $ / shares			$ 0.25		$ 1.78

Accounting Standards Updates (Details) $ in Millions	12 Months Ended
Accounting Standards Updates (Details) $ in Millions	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Recently issued accounting standards
Number of revenue streams \| item	1
Net cash provided by (used in) operating activities	$ 1,144	$ 1,911	$ 3,445
Net cash provided by (used in) financing activities	(1,090)	115	(1,809)
Forecast Adjustment \| ASU-Statement of cash flows
Recently issued accounting standards
Net cash provided by (used in) operating activities	26	69	$ 242
Net cash provided by (used in) financing activities	97	$ 61
Minimum \| Forecast Adjustment \| ASU-Leases
Recently issued accounting standards
Aggregate lease liability	65
Right-to-use asset	65
Maximum \| Forecast Adjustment \| ASU-Leases
Recently issued accounting standards
Aggregate lease liability	75
Right-to-use asset	$ 75

Variable Interest Entities (Details) - ADDCL - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Carrying amounts associated with consolidated variable interest entities
Assets	$ 716	$ 787
Liabilities	7	25
Net carrying amount	$ 709	$ 762

Drilling Fleet (Details) - USD ($) $ in Millions	12 Months Ended
Drilling Fleet (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in construction work in progress, including capital expenditures and other capital additions, such as capitalized interest
Construction work in progress, at beginning of period	$ 2,171	$ 3,735	$ 2,447
Total capital expenditures	497	1,344	2,001
Changes in accrued capital additions	(23)	(86)	(11)
Construction work in progress sold	(289)
Impairment of construction work in progress			(52)
Construction work in progress, at end of period	1,392	2,171	3,735
New builds
Changes in construction work in progress, including capital expenditures and other capital additions, such as capitalized interest
Total capital expenditures	397	1,206	1,622
Property and equipment placed into service	(896)	(2,557)
Other construction projects and capital additions
Changes in construction work in progress, including capital expenditures and other capital additions, such as capitalized interest
Total capital expenditures	100	138	379
Other property and equipment
Changes in construction work in progress, including capital expenditures and other capital additions, such as capitalized interest
Property and equipment placed into service	$ (68)	$ (265)	(650)
Deepwater Floater asset group \| Construction in Progress
Changes in construction work in progress, including capital expenditures and other capital additions, such as capitalized interest
Impairment of construction work in progress			(41)
Midwater Floater asset group \| Construction in Progress
Changes in construction work in progress, including capital expenditures and other capital additions, such as capitalized interest
Impairment of construction work in progress			$ (11)

Drilling Fleet (Disposal) (Details) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended
	May 31, 2017 item	Jun. 30, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2017 item	Dec. 31, 2017 USD ($) item $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares
Dispositions
Net cash proceeds from sale of assets						$ 350	$ 30	$ 54
Gain (loss) on the sale of assets						(1,603)	4	(36)
Assets held for sale, included in other current assets			$ 6			22	6
Assets held for sale			6			22	6
Midwater Floater asset group
Assets held and used
Loss associated with impairment		$ 94				$ 94		$ 668
Loss associated with impairment per diluted share \| $ / shares						$ 0.25		$ 1.78
Loss associated with impairment, net of tax						$ 93		$ 654
Deepwater Floater asset group
Assets held and used
Loss associated with impairment			52				$ 52	$ 507
Loss associated with impairment per diluted share \| $ / shares							$ 0.14	$ 1.31
Loss associated with impairment, tax effect							$ 0
Loss associated with impairment, net of tax								$ 481
Sale of high specification jackups
Dispositions
Disposal group operating income						65	74	208
Assets held for sale
Dispositions
Aggregate loss on impairment of assets held for sale				$ 1,400			41
Assets held for sale, included in other current assets			6			22	6
Assets held for sale			$ 6			22	6
Assets held for sale \| Rig sales
Dispositions
Aggregate loss on impairment of assets held for sale						$ 1,400	$ 41	$ 700
Aggregate loss on impairment of assets per diluted share \| $ / shares						$ 3.59	$ 0.10	$ 1.60
Aggregate loss on impairment of assets held for sale, net of tax							$ 39	$ 585
Aggregate loss on impairment of assets held for sale, tax effect						$ 0
Assets sold, not discontinued operations \| Rig sales
Dispositions
Net cash proceeds from sale of assets						22	22	35
Gain (loss) on the sale of assets						9	$ 13	$ 14
Gain (loss) on the sale of assets per diluted share \| $ / shares							$ 0.04	$ 0.02
Gain on the sale of assets, net of tax								$ 11
Assets sold, not discontinued operations \| Sale of high specification jackups
Dispositions
Number of High-Specification Jackups (in drilling units) \| item	10	10
Number of High-Specification Jackup under construction (in drilling units) \| item	5	5
Net cash proceeds from sale of assets						319
Gain (loss) on the sale of assets		$ 1,600				$ (1,600)
Gain (loss) on the sale of assets per diluted share \| $ / shares						$ 4.08
Gain (loss) on disposal of assets, tax effect						$ 0
Number of high specification jackups operated through contract completion or novation \| item	3					2
Number of high specification jackups no longer operated \| item					1
Assets sold, not discontinued operations \| Sale of other assets
Dispositions
Net cash proceeds from sale of assets						$ 9	$ 8	16
Gain (loss) on the sale of assets						$ (15)	$ (9)	(50)
Construction in Progress
Assets held and used
Loss associated with impairment								$ 52

Income Taxes (Exp) (Details) - USD ($) $ in Millions	12 Months Ended
Income Taxes (Exp) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of provision (benefit) for income taxes
Current tax expense	$ 5	$ 39	$ 254
Deferred tax expense (benefit)	89	68	(134)
Income tax expense	$ 94	$ 107	$ 120
Reconciliation of the differences between the income tax expense for the entity's continuing operations computed at the Swiss holding company statutory rate and the reported provision for income taxes
Annual effective tax rate (as a percent)	(3.10%)	11.50%	11.90%
Statutory rate	7.83%
Income tax expense (benefit)	$ (235)	$ 72	$ 80
Impairment losses subject to rates different than the Swiss federal statutory rate	241	5
Impairment losses subject to rates different than the Swiss federal statutory rate			(8)
Change in valuation allowance	162	32	10
Impact of U.S. tax reform	66
Revaluation of Norwegian assets	1	18	14
Litigation matters, primarily related to the Macondo well incident	(70)	(1)	(9)
Benefit from foreign tax credits	(15)	(16)	(10)
Changes in unrecognized tax benefits, net	(56)	(31)	12
Earnings subject to rates different than the Swiss federal statutory rate	2	34	36
Other, net	(2)	(6)	(5)
Income tax expense	$ 94	$ 107	$ 120

Income Taxes (Deferred) (Details) - USD ($) $ in Millions	12 Months Ended
Income Taxes (Deferred) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets
Net operating loss carryforwards	$ 435	$ 383
Deferred income	101	122
Accrued payroll expenses not currently deductible	54	110
Loss contingencies	42	68
Tax credit carryforwards	37	33
United Kingdom charter limitation	36	33
Professional fees	3	3
Other	30	37
Valuation allowance	(574)	(412)
Total deferred tax assets	164	377
Deferred tax liabilities
Depreciation and amortization	(157)	(239)
Other	(4)	(18)
Total deferred tax liabilities	(161)	(257)
Net deferred tax assets	3	120
U.S. foreign tax credit carryforwards	37	33
NOLs that are not subject to expiration dates	261	200
NOLs that are subject to expiration dates	174	183
Valuation allowance recorded during period	110
Reconciliation of unrecognized tax benefits, excluding interest and penalties
Balance, beginning of period	274	287	$ 272
Additions for prior year tax positions	17	13	17
Additions for current year tax positions	13	42	36
Reductions for prior year tax positions	(68)	(34)	(27)
Reductions related to statute of limitation expirations	(13)	(15)	(6)
Reductions due to settlements	(1)	(19)	(5)
Balance, end of period	222	274	287
Unrecognized tax benefits
Unrecognized tax benefits, excluding interest and penalties	222	274
Interest and penalties	87	96
Unrecognized tax benefits, including interest and penalties	309	370
Interest and penalties related to unrecognized tax benefits recognized as a component of income tax expense	(9)	$ (23)	$ (1)
Amount if recognized that would impact tax rate	$ 309

Income Taxes (US TaxReform) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statutory rate		7.83%
Increase in income tax expense due to 2017 Tax Act		$ 66
Deferred tax assets change due to 2017 Tax Act		$ (66)
U.S.
Statutory rate		35.00%
Forecast \| U.S.
Statutory rate	21.00%

Income Taxes (TaxReturns) (Details) BRL in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 BRL jurisdiction	Dec. 31, 2016 USD ($)	Dec. 31, 2015	Dec. 31, 2017 USD ($)
Income Tax Examination
Annual effective tax rate (as a percent)	(3.10%)	11.50%	11.90%
Valuation allowance \| $		$ 412		$ 574
Income Tax Examination
Number of jurisdictions with extensions beyond statute of limitations \| jurisdiction	2
Maximum number of years agreed to extensions beyond the statute of limitations	20 years
Minimum
Income Tax Examination
Range of tax returns are subject to examination	3 years
Maximum
Income Tax Examination
Range of tax returns are subject to examination	6 years
Brazil Tax Examination Assessments 2000 through 2004
Income Tax Examination
Income Tax Examination, Liability Excluding Interest and Penalties Recorded Brazil	BRL 853			258
Brazil Tax Assessments 2009 And 2010
Income Tax Examination
Income Tax Examination, Liability Excluding Interest and Penalties Recorded Brazil	BRL 145			$ 44

Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator for earnings (loss) per share, basic
Income (loss) from continuing operations attributable to controlling interest									$ (3,127)	$ 778	$ 865
Undistributed earnings allocable to participating securities										(14)	(8)
Income (loss) from continuing operations available to shareholders									$ (3,127)	$ 764	$ 857
Denominator for earnings (loss) per share, basic
Weighted-average shares outstanding	391.0	391.0	391.0	390.0	371.0	365.0	365.0	364.0	391.0	367.0	363.0
Weighted-average shares for per share calculation, basic	391.0	391.0	391.0	390.0	371.0	365.0	365.0	364.0	391.0	367.0	363.0
Per share earnings (loss) from continuing operations, basic									$ (8.00)	$ 2.08	$ 2.36
Numerator for earnings (loss) per share, diluted
Income (loss) from continuing operations attributable to controlling interest									$ (3,127)	$ 778	$ 865
Undistributed earnings allocable to participating securities										(14)	(8)
Income (loss) from continuing operations available to shareholders									$ (3,127)	$ 764	$ 857
Denominator for earnings (loss) per share, diluted
Weighted-average shares outstanding	391.0	391.0	391.0	390.0	371.0	365.0	365.0	364.0	391.0	367.0	363.0
Weighted-average shares for per share calculation, diluted	391.0	391.0	391.0	390.0	371.0	365.0	365.0	364.0	391.0	367.0	363.0
Per share earnings (loss) from continuing operations, diluted									$ (8.00)	$ 2.08	$ 2.36
Share-based awards
Anti-dilutive securities
Share-based awards excluded from earnings per share calculation (in shares)									4.7	2.5	3.3

Debt (Details) $ in Millions								1 Months Ended	3 Months Ended		12 Months Ended
Debt (Details) $ in Millions	Oct. 17, 2017 USD ($)	Oct. 16, 2017 USD ($)	May 05, 2017 USD ($)	Dec. 15, 2016 USD ($)	Dec. 08, 2016 USD ($)	Oct. 19, 2016 USD ($)	Jul. 21, 2016 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Nov. 28, 2017	Jul. 11, 2017 USD ($)	Aug. 01, 2016 USD ($)
Principal amount
Total principal amount of debt											$ 7,484	$ 8,546
Debt due within one year											257	731
Long-term debt											7,227	7,815
Carrying amount
Total debt											7,396	8,464
Debt due within one year											250	724
Long-term debt											7,146	7,740
Proceeds from issuance of debt											1,144	2,401
Restricted cash accounts and investments											466	466
Gain (loss) on retirement of debt									$ 110	$ 38	$ (55)	148	$ 23
Transocean Ltd. and Subsidiaries
Carrying amount
Percentage ownership interest in Transocean Inc. by Transocean Ltd.											100.00%
Five-Year Revolving Credit Facility
Carrying amount
Borrowing capacity, maximum								$ 3,000
Credit facility term								5 years
Consolidated indebtedness to total tangible capitalization ratio								0.6
Spread on variable rate basis (as a percent)											2.00%
Commitment fee percentage at period end											0.35%
Credit facility amount outstanding											$ 0
Letters of credit issued and outstanding											7
Credit facility available borrowing capacity											$ 3,000
Five-Year Revolving Credit Facility \| Base Rate
Carrying amount
Percentage reduction to the calculated variable rate											1.00%
Five-Year Revolving Credit Facility \| Minimum
Carrying amount
Commitment fee percentage at period end											0.15%
Five-Year Revolving Credit Facility \| Minimum \| Adjusted LIBOR
Carrying amount
Spread on variable rate basis (as a percent)											1.125%
Five-Year Revolving Credit Facility \| Maximum
Carrying amount
Commitment fee percentage at period end											0.35%
Five-Year Revolving Credit Facility \| Maximum \| Adjusted LIBOR
Carrying amount
Spread on variable rate basis (as a percent)											2.00%
2.5% Senior Notes due October 2017
Principal amount
Total principal amount of debt												485
Debt due within one year												485
Carrying amount
Total debt												484
Debt due within one year												484
Debt instrument interest rate stated percentage											2.50%
Interest rate, as adjusted (as a percent)											4.50%
Redemption price of debt instrument (as a percent)		100.00%
Aggregate principal amount repaid		$ 152									$ 62	85	180
Aggregate debt repurchase											271
Eksportfinans Loans due January 2018
Principal amount
Total principal amount of debt											26	123
Debt due within one year											26	98
Carrying amount
Total debt											26	123
Debt due within one year											$ 26	98
6.00% Senior Notes due March 2018
Principal amount
Total principal amount of debt												754
Carrying amount
Total debt												757
Debt instrument interest rate stated percentage											6.00%
Aggregate principal amount repaid											$ 354	35	211
Aggregate debt repurchase											$ 400
7.375% Senior Notes due April 2018
Principal amount
Total principal amount of debt												211
Carrying amount
Total debt												211
Debt instrument interest rate stated percentage											7.375%
Aggregate principal amount repaid											$ 83	26	10
Aggregate debt repurchase											128
6.50% Senior Notes due November 2020
Principal amount
Total principal amount of debt											286	508
Carrying amount
Total debt											$ 288	513
Debt instrument interest rate stated percentage											6.50%
Aggregate principal amount repaid											$ 15	44
Aggregate debt repurchase											207	348
6.375% Senior Notes due December 2021
Principal amount
Total principal amount of debt											328	552
Carrying amount
Total debt											$ 327	549
Debt instrument interest rate stated percentage											6.375%
Interest rate, as adjusted (as a percent)											8.375%
Aggregate principal amount repaid											$ 10	122	50
Aggregate debt repurchase											213	476
5.52% Senior Notes due May 2022
Principal amount
Total principal amount of debt											362
Debt due within one year											79
Carrying amount
Total debt											356
Debt due within one year											$ 77
Debt instrument interest rate stated percentage											5.52%
Debt instrument face value			$ 410
Proceeds from issuance of debt			$ 403
Redemption price of debt instrument (as a percent)			100.00%
Percentage of principal amount that the holder of the note may require the entity to repurchase upon the occurrence of certain events			100.00%
3.8% Senior Notes due October 2022
Principal amount
Total principal amount of debt											$ 506	539
Carrying amount
Total debt											$ 502	534
Debt instrument interest rate stated percentage											3.80%
Interest rate, as adjusted (as a percent)											5.80%
Aggregate principal amount repaid											$ 33	38	16
Aggregate debt repurchase												157
9.00% Senior Notes due July 2023
Principal amount
Total principal amount of debt											1,250	1,250
Carrying amount
Total debt											$ 1,216	1,211
Debt instrument interest rate stated percentage											9.00%
Debt instrument face value							$ 1,250
Proceeds from issuance of debt							$ 1,210
Redemption price of debt instrument (as a percent)							100.00%
7.75% Senior Secured Notes due October 2024
Principal amount
Total principal amount of debt											$ 540	600
Debt due within one year											60	60
Carrying amount
Total debt											526	583
Debt due within one year											$ 57	57
Debt instrument interest rate stated percentage											7.75%
Debt instrument face value						$ 600
Proceeds from issuance of debt						$ 583
7.75% Senior Secured Notes due October 2024 \| Maximum
Carrying amount
Maximum Collateral Ratio											5.75
6.25% Senior Notes due December 2024
Principal amount
Total principal amount of debt											$ 562	625
Debt due within one year											62	63
Carrying amount
Total debt											549	609
Debt due within one year											$ 60	60
Debt instrument interest rate stated percentage											6.25%
Debt instrument face value					$ 625
Proceeds from issuance of debt					$ 609
6.25% Senior Notes due December 2024 \| Maximum
Carrying amount
Maximum Collateral Ratio											5.75
7.50% Senior Notes due January 2026
Principal amount
Total principal amount of debt											$ 750
Carrying amount
Total debt											$ 742
Debt instrument interest rate stated percentage											7.50%
7.45% Notes due April 2027
Principal amount
Total principal amount of debt											$ 88	88
Carrying amount
Total debt											$ 86	86
Debt instrument interest rate stated percentage											7.45%
Aggregate principal amount repaid												8	4
8% Debentures due April 2027
Principal amount
Total principal amount of debt											$ 57	57
Carrying amount
Total debt											$ 57	57
Debt instrument interest rate stated percentage											8.00%
7.00% Notes due June 2028
Principal amount
Total principal amount of debt											$ 300	300
Carrying amount
Total debt											$ 307	308
Debt instrument interest rate stated percentage											7.00%			7.00%
Capital lease contract due August 2029
Principal amount
Total principal amount of debt											$ 541	566
Debt due within one year											30	25
Carrying amount
Total debt											541	566
Debt due within one year											30	25
7.5% Notes due April 2031
Principal amount
Total principal amount of debt											588	588
Carrying amount
Total debt											$ 585	585
Debt instrument interest rate stated percentage											7.50%
Debt instrument face value	$ 750
Proceeds from issuance of debt	$ 742
Redemption price of debt instrument (as a percent)	100.00%
Aggregate principal amount repaid												5	7
6.80% Senior Notes due March 2038
Principal amount
Total principal amount of debt											$ 1,000	1,000
Carrying amount
Total debt											$ 991	991
Debt instrument interest rate stated percentage											6.80%
7.35% Senior Notes due December 2041
Principal amount
Total principal amount of debt											$ 300	300
Carrying amount
Total debt											$ 297	297
Debt instrument interest rate stated percentage											7.35%
Interest rate, as adjusted (as a percent)											9.35%
Senior Secured Notes
Carrying amount
Redemption price of debt instrument (as a percent)						100.00%
Percentage of principal amount that the holder of the note may require the entity to repurchase upon the occurrence of certain events						100.00%
Restricted cash accounts and investments											$ 211	103
Aggregate carrying amount assets pledged											2,400	1,700
5.05% Senior Notes due December 2016
Carrying amount
Interest rate, as adjusted (as a percent)				5.05%
Redemption price of debt instrument (as a percent)				100.00%
Aggregate principal amount repaid				$ 938								36	25
Tendered Notes
Carrying amount
Tender Offer Principal Amount															$ 1,500	$ 1,000
Aggregate cash payment made for debt redemption											1,269	876
Gain (loss) on retirement of debt											(48)	104
Aggregate debt repurchase											1,219	981
Debt Redeemed
Carrying amount
Aggregate principal amount repaid											557	399	1,396
Aggregate cash payment made for debt redemption											564	354	1,372
Gain (loss) on retirement of debt											(7)	44	23
4.95% Senior Notes due November 2015
Carrying amount
Aggregate principal amount repaid													893
Aggregate of unspecified debt
Carrying amount
Aggregate principal amount repaid											$ 299	$ 127	$ 134

Debt (Maturities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Scheduled maturities of debt
2018	$ 257
2019	237
2020	531
2021	580
2022	687
Thereafter	5,192
Total principal amount of debt	7,484	$ 8,546
Total debt-related balances, net	(88)
Total carrying amount of debt	$ 7,396

Postemployment Benefit Plans (Assumptions) (Details) - plan	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S.
Weighted average assumptions used to determine benefit obligations
Discount rate (as a percent)	3.68%	4.26%
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate (as a percent)	4.26%	4.56%	4.16%
Expected rate of return (as a percent)	6.31%	6.82%	7.79%
Compensation trend rate (as a percent)		0.22%	0.21%
Non-U.S. Plans
Weighted average assumptions used to determine benefit obligations
Discount rate (as a percent)	2.49%	2.69%
Compensation trend rate (as a percent)	2.50%	2.25%
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate (as a percent)	2.69%	3.69%	3.26%
Expected rate of return (as a percent)	4.79%	5.85%	5.93%
Compensation trend rate (as a percent)	2.25%	4.01%	3.83%
OPEB Plans
Weighted average assumptions used to determine benefit obligations
Discount rate (as a percent)	2.93%	3.08%
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate (as a percent)	3.08%	3.13%	3.86%
Health care cost trend rate, initial (as a percent)			7.81%
Health care cost trend rate, ultimate (as a percent)			5.00%
Funded Plan \| U.S.
Postemployment Benefit Plans
Number of benefit plans	3	1
Funded Plan \| U.K.
Postemployment Benefit Plans
Number of benefit plans	1
Funded Plan \| Norway
Postemployment Benefit Plans
Number of benefit plans	2	4
Unfunded Plan \| U.S.
Postemployment Benefit Plans
Number of benefit plans	3
Unfunded Plan \| Norway
Postemployment Benefit Plans
Number of benefit plans	2

Postemployment Benefit Plans (Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net periodic benefit costs, before tax
Service cost	$ 6	$ 13
Interest cost	76	87
Net periodic benefit costs	5	(11)	$ 26
Transocean Plans
Net periodic benefit costs, before tax
Service cost	6	13	31
Interest cost	76	86	84
Expected return on plan assets	(94)	(105)	(115)
Settlements and curtailments	13	(5)	5
Actuarial (gain) loss, net	6	4	22
Net periodic benefit costs	7	(7)	27
OPEB Plans
Net periodic benefit costs, before tax
Interest cost		1
Net periodic benefit costs	(2)	(4)	(1)
U.S. \| Transocean Plans
Net periodic benefit costs, before tax
Service cost	3	3	5
Interest cost	65	69	65
Expected return on plan assets	(74)	(80)	(87)
Settlements and curtailments			3
Actuarial (gain) loss, net	5	5	11
Net periodic benefit costs	(1)	(3)	(3)
Non-U.S. Plans \| Transocean Plans
Net periodic benefit costs, before tax
Service cost	3	10	26
Interest cost	11	17	19
Expected return on plan assets	(20)	(25)	(28)
Settlements and curtailments	13	(5)	2
Actuarial (gain) loss, net	1	(1)	11
Net periodic benefit costs	$ 8	$ (4)	$ 30

Postemployment Benefit Plans (AOCI) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Unrecognized accumulated other comprehensive income, before tax
Actuarial gain (loss), net	$ (389)	$ (413)
Prior service cost, net	23	26
Total	(366)	(387)
Accumulated other comprehensive income expected to be recognized during the next fiscal year
Actuarial loss, net	9
Prior service cost, net	(3)
Total amount expected to be recognized	6
OPEB Plans
Unrecognized accumulated other comprehensive income, before tax
Actuarial gain (loss), net	(4)	(3)
Prior service cost, net	23	26
Total	19	23
Accumulated other comprehensive income expected to be recognized during the next fiscal year
Actuarial loss, net	1
Prior service cost, net	(3)
Total amount expected to be recognized	(2)
U.S. \| Transocean Plans
Unrecognized accumulated other comprehensive income, before tax
Actuarial gain (loss), net	(301)	(316)
Total	(301)	(316)
Accumulated other comprehensive income expected to be recognized during the next fiscal year
Actuarial loss, net	7
Total amount expected to be recognized	7
Non-U.S. Plans \| Transocean Plans
Unrecognized accumulated other comprehensive income, before tax
Actuarial gain (loss), net	(84)	(94)
Total	(84)	$ (94)
Accumulated other comprehensive income expected to be recognized during the next fiscal year
Actuarial loss, net	1
Total amount expected to be recognized	$ 1

Postemployment Benefit Plans (Funded) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in projected benefit obligation
Projected benefit obligation, beginning of period	$ 1,974	$ 2,049
Actuarial (gains) losses, net	135	85
Service cost	6	13
Interest cost	76	87
Currency exchange rate changes	35	(77)
Participant contributions		1
Benefits paid	(148)	(140)
Settlements and curtailments		(44)
Projected benefit obligation, end of period	2,078	1,974	$ 2,049
Change in plan assets
Fair value of plan assets, beginning of period	1,604	1,637
Actual return on plan assets	229	177
Currency exchange rate changes	36	(80)
Employer contributions	15	49
Participant contributions		1
Benefits paid	(148)	(140)
Settlements		(40)
Fair value of plan assets, end of period	1,736	1,604	1,637
Funded status, end of period	(342)	(370)
Balance sheet classification, end of period:
Pension asset, non-current	17	5
Pension liability, current	(6)	(5)
Pension liability, non-current	(353)	(370)
Accumulated other comprehensive income (loss)	(366)	(387)
Aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	1,704	1,581
Fair value of plan assets	1,345	1,206
Aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	1,702	1,580
Fair value of plan assets	1,343	1,204
Transocean Plans
Change in projected benefit obligation
Service cost	6	13	31
Interest cost	76	86	84
Change in plan assets
Fair value of plan assets, beginning of period	1,604
Fair value of plan assets, end of period	1,736	1,604
Accumulated benefit obligation for all defined benefit pension plans
Accumulated benefit obligation	2,100	2,000
Transocean Plans \| U.S.
Change in projected benefit obligation
Projected benefit obligation, beginning of period	1,557	1,523
Actuarial (gains) losses, net	115	52
Service cost	3	3	5
Interest cost	65	69	65
Benefits paid	(60)	(90)
Projected benefit obligation, end of period	1,680	1,557	1,523
Change in plan assets
Fair value of plan assets, beginning of period	1,204	1,198
Actual return on plan assets	198	93
Employer contributions	1	3
Benefits paid	(60)	(90)
Fair value of plan assets, end of period	1,343	1,204	1,198
Funded status, end of period	(337)	(353)
Balance sheet classification, end of period:
Pension liability, current	(2)	(2)
Pension liability, non-current	(335)	(351)
Accumulated other comprehensive income (loss)	(301)	(316)
Aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	1,680	1,557
Fair value of plan assets	1,343	1,204
Aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	1,680	1,557
Fair value of plan assets	1,343	1,204
Transocean Plans \| Non-U.S. Plans
Change in projected benefit obligation
Projected benefit obligation, beginning of period	398	502
Actuarial (gains) losses, net	18	36
Service cost	3	10	26
Interest cost	11	17	19
Currency exchange rate changes	35	(77)
Benefits paid	(86)	(46)
Settlements and curtailments		(44)
Projected benefit obligation, end of period	379	398	502
Change in plan assets
Fair value of plan assets, beginning of period	400	439
Actual return on plan assets	31	84
Currency exchange rate changes	36	(80)
Employer contributions	12	43
Benefits paid	(86)	(46)
Settlements		(40)
Fair value of plan assets, end of period	393	400	439
Funded status, end of period	14	2
Balance sheet classification, end of period:
Pension asset, non-current	17	5
Pension liability, current	(1)
Pension liability, non-current	(2)	(3)
Accumulated other comprehensive income (loss)	(84)	(94)
Aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	5	5
Fair value of plan assets	2	2
Aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	3	4
OPEB Plans
Change in projected benefit obligation
Projected benefit obligation, beginning of period	19	24
Actuarial (gains) losses, net	2	(3)
Interest cost		1
Participant contributions		1
Benefits paid	(2)	(4)
Projected benefit obligation, end of period	19	19	$ 24
Change in plan assets
Employer contributions	2	3
Participant contributions		1
Benefits paid	(2)	(4)
Funded status, end of period	(19)	(19)
Balance sheet classification, end of period:
Pension liability, current	(3)	(3)
Pension liability, non-current	(16)	(16)
Accumulated other comprehensive income (loss)	19	23
Aggregate projected benefit obligation and fair value of plan assets for plans with a projected benefit obligation in excess of plan assets
Projected benefit obligation	19	19
Aggregate accumulated benefit obligation and fair value of plan assets for plans with an accumulated benefit obligation in excess of plan assets
Accumulated benefit obligation	$ 19	$ 19

Postemployment Benefit Plans (Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair value of plan assets
Total investments	$ 1,736	$ 1,604	$ 1,637
Projected pension benefits payments
2018	82
2019	83
2020	86
2021	89
2022	91
2023-2027	$ 488
U.S.
Weighted-average target allocations of the investments
Total target allocation percentage	100.00%	100.00%
Total actual allocation percentage	100.00%	100.00%
U.S. \| Equity securities
Weighted-average target allocations of the investments
Total target allocation percentage	50.00%	50.00%
Total actual allocation percentage	52.00%	53.00%
U.S. \| Fixed income securities
Weighted-average target allocations of the investments
Total target allocation percentage	50.00%	50.00%
Total actual allocation percentage	48.00%	47.00%
Non-U.S. Plans
Weighted-average target allocations of the investments
Total target allocation percentage	100.00%	100.00%
Total actual allocation percentage	100.00%	100.00%
Non-U.S. Plans \| Equity securities
Weighted-average target allocations of the investments
Total target allocation percentage	39.00%	45.00%
Total actual allocation percentage	39.00%	45.00%
Non-U.S. Plans \| Fixed income securities
Weighted-average target allocations of the investments
Total target allocation percentage	50.00%	45.00%
Total actual allocation percentage	48.00%	44.00%
Non-U.S. Plans \| Other investments
Weighted-average target allocations of the investments
Total target allocation percentage	11.00%	10.00%
Total actual allocation percentage	13.00%	11.00%
Transocean Plans
Fair value of plan assets
Total investments	$ 1,736	$ 1,604
Defined benefit plan contributions funded by cash flows from operations
Expected defined plan contributions next year	12
Transocean Plans \| Significant observable inputs
Fair value of plan assets
Total investments	1,337	1,200
Transocean Plans \| Significant other observable inputs
Fair value of plan assets
Total investments	399	404
Transocean Plans \| Mutual funds
Fair value of plan assets
Total investments	1,680	1,561
Transocean Plans \| Mutual funds \| Significant observable inputs
Fair value of plan assets
Total investments	1,324	1,196
Transocean Plans \| Mutual funds \| Significant other observable inputs
Fair value of plan assets
Total investments	356	365
Transocean Plans \| U.S. equity funds
Fair value of plan assets
Total investments	557	518
Transocean Plans \| U.S. equity funds \| Significant observable inputs
Fair value of plan assets
Total investments	557	516
Transocean Plans \| U.S. equity funds \| Significant other observable inputs
Fair value of plan assets
Total investments		2
Transocean Plans \| Non-U.S. equity funds
Fair value of plan assets
Total investments	296	298
Transocean Plans \| Non-U.S. equity funds \| Significant observable inputs
Fair value of plan assets
Total investments	138	113
Transocean Plans \| Non-U.S. equity funds \| Significant other observable inputs
Fair value of plan assets
Total investments	158	185
Transocean Plans \| Bond funds
Fair value of plan assets
Total investments	827	745
Transocean Plans \| Bond funds \| Significant observable inputs
Fair value of plan assets
Total investments	629	567
Transocean Plans \| Bond funds \| Significant other observable inputs
Fair value of plan assets
Total investments	198	178
Transocean Plans \| Other investments
Fair value of plan assets
Total investments	56	43
Transocean Plans \| Other investments \| Significant observable inputs
Fair value of plan assets
Total investments	13	4
Transocean Plans \| Other investments \| Significant other observable inputs
Fair value of plan assets
Total investments	43	39
Transocean Plans \| Cash and money market funds
Fair value of plan assets
Total investments	13	4
Transocean Plans \| Cash and money market funds \| Significant observable inputs
Fair value of plan assets
Total investments	13	4
Transocean Plans \| Property collective trusts
Fair value of plan assets
Total investments	20	17
Transocean Plans \| Property collective trusts \| Significant other observable inputs
Fair value of plan assets
Total investments	20	17
Transocean Plans \| Investment contracts
Fair value of plan assets
Total investments	23	22
Transocean Plans \| Investment contracts \| Significant other observable inputs
Fair value of plan assets
Total investments	23	22
Transocean Plans \| U.S.
Fair value of plan assets
Total investments	1,343	1,204	1,198
Projected pension benefits payments
2018	71
2019	73
2020	75
2021	79
2022	80
2023-2027	421
Transocean Plans \| U.S. \| Significant observable inputs
Fair value of plan assets
Total investments	1,330	1,198
Transocean Plans \| U.S. \| Significant other observable inputs
Fair value of plan assets
Total investments	13	6
Transocean Plans \| U.S. \| Mutual funds
Fair value of plan assets
Total investments	1,337	1,202
Transocean Plans \| U.S. \| Mutual funds \| Significant observable inputs
Fair value of plan assets
Total investments	1,324	1,196
Transocean Plans \| U.S. \| Mutual funds \| Significant other observable inputs
Fair value of plan assets
Total investments	13	6
Transocean Plans \| U.S. \| U.S. equity funds
Fair value of plan assets
Total investments	557	518
Transocean Plans \| U.S. \| U.S. equity funds \| Significant observable inputs
Fair value of plan assets
Total investments	557	516
Transocean Plans \| U.S. \| U.S. equity funds \| Significant other observable inputs
Fair value of plan assets
Total investments		2
Transocean Plans \| U.S. \| Non-U.S. equity funds
Fair value of plan assets
Total investments	143	117
Transocean Plans \| U.S. \| Non-U.S. equity funds \| Significant observable inputs
Fair value of plan assets
Total investments	138	113
Transocean Plans \| U.S. \| Non-U.S. equity funds \| Significant other observable inputs
Fair value of plan assets
Total investments	5	4
Transocean Plans \| U.S. \| Bond funds
Fair value of plan assets
Total investments	637	567
Transocean Plans \| U.S. \| Bond funds \| Significant observable inputs
Fair value of plan assets
Total investments	629	567
Transocean Plans \| U.S. \| Bond funds \| Significant other observable inputs
Fair value of plan assets
Total investments	8
Transocean Plans \| U.S. \| Other investments
Fair value of plan assets
Total investments	6	2
Transocean Plans \| U.S. \| Other investments \| Significant observable inputs
Fair value of plan assets
Total investments	6	2
Transocean Plans \| U.S. \| Cash and money market funds
Fair value of plan assets
Total investments	6	2
Transocean Plans \| U.S. \| Cash and money market funds \| Significant observable inputs
Fair value of plan assets
Total investments	6	2
Transocean Plans \| Non-U.S. Plans
Fair value of plan assets
Total investments	393	400	$ 439
Projected pension benefits payments
2018	8
2019	7
2020	8
2021	8
2022	9
2023-2027	60
Transocean Plans \| Non-U.S. Plans \| Significant observable inputs
Fair value of plan assets
Total investments	7	2
Transocean Plans \| Non-U.S. Plans \| Significant other observable inputs
Fair value of plan assets
Total investments	386	398
Transocean Plans \| Non-U.S. Plans \| Mutual funds
Fair value of plan assets
Total investments	343	359
Transocean Plans \| Non-U.S. Plans \| Mutual funds \| Significant other observable inputs
Fair value of plan assets
Total investments	343	359
Transocean Plans \| Non-U.S. Plans \| Non-U.S. equity funds
Fair value of plan assets
Total investments	153	181
Transocean Plans \| Non-U.S. Plans \| Non-U.S. equity funds \| Significant other observable inputs
Fair value of plan assets
Total investments	153	181
Transocean Plans \| Non-U.S. Plans \| Bond funds
Fair value of plan assets
Total investments	190	178
Transocean Plans \| Non-U.S. Plans \| Bond funds \| Significant other observable inputs
Fair value of plan assets
Total investments	190	178
Transocean Plans \| Non-U.S. Plans \| Other investments
Fair value of plan assets
Total investments	50	41
Transocean Plans \| Non-U.S. Plans \| Other investments \| Significant observable inputs
Fair value of plan assets
Total investments	7	2
Transocean Plans \| Non-U.S. Plans \| Other investments \| Significant other observable inputs
Fair value of plan assets
Total investments	43	39
Transocean Plans \| Non-U.S. Plans \| Cash and money market funds
Fair value of plan assets
Total investments	7	2
Transocean Plans \| Non-U.S. Plans \| Cash and money market funds \| Significant observable inputs
Fair value of plan assets
Total investments	7	2
Transocean Plans \| Non-U.S. Plans \| Property collective trusts
Fair value of plan assets
Total investments	20	17
Transocean Plans \| Non-U.S. Plans \| Property collective trusts \| Significant other observable inputs
Fair value of plan assets
Total investments	20	17
Transocean Plans \| Non-U.S. Plans \| Investment contracts
Fair value of plan assets
Total investments	23	22
Transocean Plans \| Non-U.S. Plans \| Investment contracts \| Significant other observable inputs
Fair value of plan assets
Total investments	23	$ 22
OPEB Plans
Defined benefit plan contributions funded by cash flows from operations
Expected defined plan contributions next year	3
Projected pension benefits payments
2018	3
2019	3
2020	3
2021	2
2022	2
2023-2027	$ 7

Postemployment Benefit Plans (DefCont) (Details) $ in Millions		12 Months Ended
	Jan. 01, 2017	Dec. 31, 2017 USD ($) plan	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Contribution Plan Disclosure [Line Items]
Number of defined contribution plans sponsored by the entity (in plans) \| plan		4
Contribution expense \| $		$ 43	$ 51	$ 89
U.S. Savings Plan \| Qualified plan
Defined Contribution Plan Disclosure [Line Items]
Matching contribution as a percentage of participant's base salary		10.00%
Non-U.S. Savings Plan \| Nonqualified plan
Defined Contribution Plan Disclosure [Line Items]
Matching contribution as a percentage of participant's base salary	6.00%	12.00%
Minimum \| U.K. Savings Plan \| Qualified plan
Defined Contribution Plan Disclosure [Line Items]
Matching contribution as a percentage of participant's base salary		4.50%
Minimum \| Non-U.S. Savings Plan \| Nonqualified plan
Defined Contribution Plan Disclosure [Line Items]
Additional matching contribution as a percentage of participant's base salary		4.50%
Maximum \| U.K. Savings Plan \| Qualified plan
Defined Contribution Plan Disclosure [Line Items]
Matching contribution as a percentage of participant's base salary		9.50%
Maximum \| Non-U.S. Savings Plan \| Nonqualified plan
Defined Contribution Plan Disclosure [Line Items]
Additional matching contribution as a percentage of participant's base salary		6.50%

Commitments and Contingencies (Leases) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Rental expenses for all leases, including leases with terms of less than one year	$ 52,000,000	$ 45,000,000	$ 72,000,000
Depreciation expense for assets held under capital lease	23,000,000	23,000,000	$ 23,000,000
Aggregate carrying amount of assets held under capital lease
Property and equipment, cost	774,000,000	776,000,000
Accumulated depreciation	(170,000,000)	(149,000,000)
Property and equipment, net	604,000,000	$ 627,000,000
Capital lease, future minimum rental payments
2018	72,000,000
2019	72,000,000
2020	72,000,000
2021	71,000,000
2022	71,000,000
Thereafter	479,000,000
Total future minimum rental payment	837,000,000
Less amount representing imputed interest	(296,000,000)
Present value of future minimum rental payments under capital leases	541,000,000
Less current portion included in debt due within one year	(30,000,000)
Long-term capital lease obligation	511,000,000
Operating leases, future minimum rental payments
2018	15,000,000
2019	12,000,000
2020	11,000,000
2021	10,000,000
2022	10,000,000
Thereafter	39,000,000
Total future minimum rental payment	$ 97,000,000
Capital lease contract due August 2029
Debt Instrument [Line Items]
Implicit interest rate (as a percent)	7.80%
Scheduled monthly payments under capital lease obligation	$ 6,000,000
End of lease obligation	$ 1

Commitments and Contingencies (PurchOb) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Letters of credit and surety bonds
Letters of credit and surety bonds
Outstanding letters of credit	$ 29	$ 50
Aggregate cash collateral	7
Surety bonds outstanding	51	$ 33
Supply agreement
Future Purchase obligations
2018	67
2019	100
2020	107
2021	99
2022	102
Thereafter	584
Total	1,059
New builds
Future Purchase obligations
2018	48
2019	3
2020	847
Total	$ 898

Commitments and Contingencies (Cont) (Details) $ / shares in Units, BRL in Millions, $ in Millions				1 Months Ended					3 Months Ended	12 Months Ended
	Nov. 28, 2017 USD ($)	May 29, 2015 USD ($) item	Jan. 03, 2013 USD ($) item	Nov. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Aug. 31, 2015 USD ($)	Jun. 30, 2014	Oct. 31, 2007 subsidiary	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2017 BRL plaintiff lawsuit subsidiary	Dec. 31, 2017 USD ($) plaintiff lawsuit subsidiary
Contingencies
Recoveries from insurance									$ 30
Five-Year Revolving Credit Facility
Other legal proceedings
Credit facility term							5 years
7.00% Notes due June 2028
Other legal proceedings
Debt instrument interest rate stated percentage	7.00%												7.00%	7.00%
Macondo well incident
Contingencies
Income recognized in connection with settlement agreement												$ 788
Income recognized in connection with settlement agreement, net of tax												$ 735
Income recognized in connection with settlement agreement, diluted, (in dollars per share) \| $ / shares												$ 2.02
Decrease in other current liabilities from settlement of contingencies												$ 125
Amount of fines, recoveries and civil penalties									250		$ 250			$ 219
Settlement, legal fees												125
Recoveries from insurance												538
Macondo well incident \| Plea Agreement
Contingencies
Number of subsidiaries that pled guilty to charges \| item			1
Number of misdemeanor count of negligently discharging oil \| item			1
Amount outstanding under the Plea Agreement									60		60
Amount paid for obligations under the Plea Agreement and Consent Decree including interest			$ 400							$ 60	60	60
Macondo well incident \| Consent Decree
Contingencies
Amount of fines, recoveries and civil penalties			$ 1,000
Amount paid for obligations under the Plea Agreement and Consent Decree including interest												$ 204
PSC Settlement Agreement
Contingencies
Settlement agreement subject to court approval		$ 212
Settlement, legal fees		$ 25
Number of classes of plaintiffs \| item		2
Settlement allocated to Punitive Damage Class (as a percent)		72.80%
Settlement allocated to Assigned Claims Class (as a percent)		27.20%
Number of claimants opted out of settlement agreement \| item		30
Cash payment into an escrow account pending approval by MDL Court					$ 25	$ 212
Cash released from escrow account by MDL Court				$ 25
Escrow Deposit									$ 237		$ 237			$ 212
Asbestos litigation \| LA
Other legal proceedings
Number of pending separate lawsuits remained, each with a single plaintiff \| plaintiff													8	8
Asbestos litigation \| Wrongful death and personal injury
Other legal proceedings
Number of subsidiaries involved in lawsuits arising from design, construction and refurbishment of major industrial complexes \| subsidiary													1	1
Number of lawsuits alleging personal injury from asbestos exposure for subsidiary involved in design, construction and refurbishment of major industrial complexes \| lawsuit													140	140
Insurance limits potentially available for damages in lawsuits regarding personal injury from asbestos exposure for subsidiary involved in design, construction and refurbishment of major industrial														$ 1,000
Rio de Janeiro tax assessment
Other legal proceedings
Tax assessment from state tax authorities													BRL 529	$ 160
Nigerian Cabotage Act litigation
Other legal proceedings
Number of subsidiaries that were served a Notice and Demand from the Nigeria Maritime Administration and Safety Agency (NIMASA) \| subsidiary								3
Percentage of surcharge on the value of contracts performed in Nigeria pursuant to the Coastal and Inland Shipping (Cabotage) Act 2003 (the Cabotage Act)								2.00%
Global Marine Litigation \| Five-Year Revolving Credit Facility
Other legal proceedings
Credit facility term	5 years
Global Marine Litigation \| 7.00% Notes due June 2028
Other legal proceedings
Debt instrument face value	$ 300
Hazardous waste disposal sites
Other legal proceedings
Percentage of liability for remediation and related costs													8.00%	8.00%
Number of subsidiaries ordered by California Regional Water Quality Control Board to develop testing plan for Alhambra, California site \| subsidiary													1	1
Hazardous waste disposal sites \| Minimum
Other legal proceedings
Minimum number of subsidiaries likely to be named potentially responsible party by US Environmental Protection Agency for superfund site (in counts) \| subsidiary													1	1

Noncontrolling Interest (Redeemable) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Redeemable noncontrolling interest
Balance, beginning of period	$ 28	$ 5	$ 11
Net income (loss) attributable to noncontrolling interest	30	23	(6)
Balance, end of period	$ 58	$ 28	$ 5
ADDCL
Redeemable noncontrolling interest
Ownership percentage	65.00%
ADDCL \| Angco Cayman Limited
Redeemable noncontrolling interest
Ownership percentage	35.00%

Noncontrolling Interest (Details) - USD ($) $ in Millions		12 Months Ended
Noncontrolling Interest (Details) - USD ($) $ in Millions	Dec. 09, 2016	Dec. 31, 2016	Dec. 31, 2015
Noncontrolling interest
Distribution to holders of noncontrolling interest		$ 30	$ 29
Total number of securities issued in merger	1.20
Total number of securities issued in merger	23,800,000
Transocean Partners Llc
Noncontrolling interest
Dividends		99	100
Distribution to holders of noncontrolling interest		$ 28	$ 29

Shareholders' Equity (Details) SFr / shares in Units, $ / shares in Units, $ in Millions, SFr in Billions				1 Months Ended		9 Months Ended	12 Months Ended
	Dec. 09, 2016 shares	Jan. 07, 2016 shares	Mar. 18, 2015 USD ($)	May 31, 2015 USD ($) installment $ / shares	May 31, 2009 CHF (SFr)	Sep. 30, 2015 USD ($) item	Dec. 31, 2015 USD ($) shares	Dec. 31, 2017 subsidiary SFr / shares shares	Dec. 31, 2016 SFr / shares shares	Oct. 29, 2015 SFr / shares	Oct. 29, 2015 USD ($)	May 31, 2014 installment $ / shares
Par value reduction
Approved par value of common stock (in Swiss francs per share) \| SFr / shares										SFr 0.10
Par value of common stock (in Swiss francs per share) \| SFr / shares								SFr 0.10	SFr 0.10	SFr 15.00
Distribution of qualifying additional paid-in capital
Cash distribution approved in the form of additional paid-in capital (in dollars per share) \| $ / shares				$ 0.60								$ 3.00
Number of quarterly installments (in installments) \| installment				4								4
Amount of installment (in dollars per share) \| $ / shares				$ 0.15								$ 0.75
Liability for distribution payable \| $				$ 218
Number of installments paid (in installments) \| item						2
Installment of dividend paid \| $			$ 272			$ 109	$ 381
Cancellation of previously declared dividend \| $											$ 109
Total number of securities issued in merger	23,800,000
Total number of securities issued in merger	1.20
Shares held in treasury
Authorized amount for repurchase of shares \| SFr					SFr 3.5
Shares repurchased and cancelled (in shares)		2,900,000
Treasury shares							2,900,000
Shares held by subsidiary
Number of subsidiaries to whom shares were issued \| subsidiary								2
Number of shares held by subsidiary								3,600,000	5,400,000

Shareholders' Equity (AOCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Changes in accumulated other comprehensive loss, presented net of tax
Balance, beginning of period	$ (283)
Balance, end of period	(290)	$ (283)
Defined benefit pension plans
Changes in accumulated other comprehensive loss, presented net of tax
Balance, beginning of period	(283)	(277)
Other comprehensive income (loss) before reclassifications	(2)	(15)
Reclassifications to net income	(5)	9
Other comprehensive income, net	(7)	(6)
Balance, end of period	$ (290)	$ (283)

Share-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share Based Compensation
Shares authorized under the plan	20,700,000
Shares available for grant under the plan	9,900,000
General term of awards after they are vested	7 years
Total unrecognized compensation costs related to all unvested share based awards	$ 43
Weighted average period over compensation costs are expected to be recognized	1 year 8 months 12 days
Time-based awards
Share Based Compensation
Vesting period	3 years
Performance-based awards
Share Based Compensation
Vesting period	1 year
Measurement period	3 years
Restricted shares \| Time-based awards
Equity instruments other than options activity
Outstanding at the beginning of the period (in shares)	4,006,082
Granted (in shares)	1,921,029	3,155,382	2,848,521
Vested (in shares)	(1,867,970)	(1,725,734)	(1,817,758)
Forfeited (in shares)	(238,686)
Outstanding at the end of the period (in shares)	3,820,455	4,006,082
Weighted-average grant-date fair value per share
Outstanding at the beginning of the period (in dollars per share)	$ 13.10
Granted (in dollars per share)	13.03	$ 8.69	$ 18.70
Vested (in dollars per share)	15.14
Forfeited (in dollars per share)	11.42
Outstanding at the end of the period (in dollars per share)	$ 12.15	$ 13.10
Total grant date fair value	$ 28	$ 48	$ 81
Restricted shares \| Performance-based awards
Equity instruments other than options activity
Outstanding at the beginning of the period (in shares)	1,439,606
Granted (in shares)	689,740	997,362	652,592
Vested (in shares)	(478,492)
Forfeited (in shares)	(12,173)
Outstanding at the end of the period (in shares)	1,638,681	1,439,606
Weighted-average grant-date fair value per share
Outstanding at the beginning of the period (in dollars per share)	$ 14.40
Granted (in dollars per share)	16.25	$ 11.60	$ 17.91
Vested (in dollars per share)	13.87
Forfeited (in dollars per share)	11.60
Outstanding at the end of the period (in dollars per share)	$ 13.56	$ 14.40
Total grant date fair value	$ 7	$ 6	$ 0
Stock options \| Time-based awards
Stock option activity
Outstanding at the beginning of the period (in shares)	1,934,695
Granted (in shares)	877,231	945,724
Exercised (in shares)	0	0	0
Forfeited (in shares)	(58,463)
Outstanding at the end of the period (in shares)	2,753,463	1,934,695
Vested and exercisable at the end of the period (in shares)	1,263,702
Weighted-average exercise price per share
Outstanding at the beginning of the period (in dollars per share)	$ 44.88
Granted (in dollars per share)	6.46	$ 5.11
Outstanding at the end of the period (in dollars per share)	34.98	$ 44.88
Vested and exercisable at the end of the period (in dollars per share)	$ 62.78
Weighted-average remaining contractual term
Outstanding	6 years 4 months 13 days	6 years 1 month 13 days
Vested and exercisable at the end of the period	3 years 7 months 17 days
Aggregate intrinsic value (in millions)
Aggregate intrinsic value	$ 2	$ 6
Additional disclosure
Total grant-date fair value of awards vested	$ 2	$ 3	$ 9
Unvested stock options outstanding (in shares)	1,489,761

Supplemental Balance Sheet Information (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Other current liabilities
Accrued payroll and employee benefits	$ 176	$ 200
Accrued interest	127	135
Accrued taxes, other than income	67	87
Macondo well incident settlement obligations		60
Deferred revenues	213	209
Contingent liabilities	246	262
Other	10	7
Total other current liabilities	839	960
Other long-term liabilities
Postemployment benefit plan obligations	353	370
Income taxes payable	247	333
Deferred revenues	422	390
Other	60	60
Total other long-term liabilities	$ 1,082	$ 1,153

Supplemental Cash Flow Information (Details) - USD ($) shares in Millions, $ in Millions		12 Months Ended
	Dec. 09, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in operating assets and liabilities
Decrease in accounts receivable		$ 230	$ 350	$ 742
Increase in other current assets		(30)	(29)	(177)
(Increase) decrease in other assets		(33)	(12)	5
Decrease in accounts payable and other current liabilities		(115)	(286)	(828)
Decrease in other long-term liabilities		(13)	(55)	(72)
Change in income taxes receivable / payable, net		(58)	(133)	(65)
Net change in operating assets and liabilities		(19)	(165)	(395)
Certain cash operating activities
Cash payments for interest		486	351	439
Cash payments for income taxes		124	172	314
Non-cash investing and financing activities
Capital additions, accrued at end of period		$ 20	42	$ 128
Issuance of shares for acquisition of noncontrolling interest			$ 317
Issuance of shares for acquisition of noncontrolling interest (in shares)	23.8

Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financial instruments
Carrying amount of restricted cash and investments	$ 489	$ 510
Carrying amount of long-term debt, including current maturities	7,396	8,464
Carrying amount of cash equivalents	2,100	2,600
Carrying amount
Financial instruments
Cash and cash equivalents	2,519	3,052
Short-term investments	450
Carrying amount of restricted cash and investments	489	510
Carrying amount of long-term debt, including current maturities	7,396	8,464
Fair value
Financial instruments
Cash and cash equivalents	2,519	3,052
Short-term investments	450
Restricted cash accounts and investments	489	511
Long-term debt, including current maturities	7,538	8,218
Eksportfinans Loans due January 2018
Financial instruments
Carrying amount of restricted cash and investments	33	123
Carrying amount of long-term debt, including current maturities	26	123
Certain contingent obligations
Financial instruments
Carrying amount of restricted cash and investments	456	387
Certain contingent obligations \| Other current assets
Financial instruments
Carrying amount of restricted cash and investments	440	368
Certain contingent obligations \| Other assets
Financial instruments
Carrying amount of restricted cash and investments	16	19
Significant other observable inputs \| Eksportfinans Loans due January 2018
Financial instruments
Restricted cash accounts and investments	$ 33	$ 124

Risk Concentration (Details)	12 Months Ended
Risk Concentration (Details)	Dec. 31, 2017 employee
Labor Agreements
Number of employees	4,900
Number of employees engaged through contract labor providers	400
Unionized Employees \| Workforce Subject to Collective Bargaining
Labor Agreements
Percentage of concentration	26.00%

Operating Segments, Geographic Analysis and Major Customers (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Operating segments, geographical analysis and major customers
Number of operating segments \| segment									1
Operating revenues	$ 629	$ 808	$ 751	$ 785	$ 974	$ 906	$ 940	$ 1,341	$ 2,973	$ 4,161	$ 7,386
U.S.
Operating segments, geographical analysis and major customers
Operating revenues									1,527	1,977	2,416
Brazil
Operating segments, geographical analysis and major customers
Operating revenues									335	453	673
U.K.
Operating segments, geographical analysis and major customers
Operating revenues									288	551	1,139
Other countries
Operating segments, geographical analysis and major customers
Operating revenues									$ 823	$ 1,180	$ 3,158

Operating Segments, Geographic Analysis and Major Customers (Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Operating segments, geographical analysis and major customers
Long-lived assets	$ 17,402	$ 21,093
U.S.
Operating segments, geographical analysis and major customers
Long-lived assets	7,541	6,181
Trinidad
Operating segments, geographical analysis and major customers
Long-lived assets	2,563	3,977
Other countries
Operating segments, geographical analysis and major customers
Long-lived assets	7,298	10,935
Switzerland
Operating segments, geographical analysis and major customers
Long-lived assets		$ 2
Maximum \| Switzerland
Operating segments, geographical analysis and major customers
Long-lived assets	$ 1

Operating Segments, Geographic Analysis and Major Customers (Concentration) (Details) - Total operating revenues - Operating revenues	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Chevron Corporation
Concentration Risk
Percentage of concentration	29.00%	24.00%	14.00%
Shell
Concentration Risk
Percentage of concentration	17.00%	12.00%	10.00%
Petrobras
Concentration Risk
Percentage of concentration	14.00%	11.00%
BP
Concentration Risk
Percentage of concentration		12.00%

Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Results (Unaudited)
Operating revenues	$ 629	$ 808	$ 751	$ 785	$ 974	$ 906	$ 940	$ 1,341	$ 2,973	$ 4,161	$ 7,386
Operating income (loss)	12	(1,145)	(1,544)	173	316	229	163	424	(2,504)	1,132	1,365
Income (loss) from continuing operations	(102)	(1,411)	(1,679)	95	257	236	92	242	(3,097)	827	895
Net income (loss)	(102)	(1,411)	(1,679)	95	257	236	93	241	(3,097)	827	897
Net income (loss) attributable to controlling interest	$ (111)	$ (1,417)	$ (1,690)	$ 91	$ 243	$ 218	$ 82	$ 235	$ (3,127)	$ 778	$ 865
Per share earnings (loss) from continuing operations
Basic (in dollars per share)	$ (0.28)	$ (3.62)	$ (4.32)	$ 0.23	$ 0.64	$ 0.59	$ 0.22	$ 0.64	$ (8.00)	$ 2.08	$ 2.36
Diluted (in dollars per share)	$ (0.28)	$ (3.62)	$ (4.32)	$ 0.23	$ 0.64	$ 0.59	$ 0.22	$ 0.64	$ (8.00)	$ 2.08	$ 2.36
Weighted-average shares outstanding
Basic (in shares)	391	391	391	390	371	365	365	364	391	367	363
Diluted (in shares)	391	391	391	390	371	365	365	364	391	367	363

Quarterly Results (Unaudited) (Explanatory) (Details) $ in Millions	3 Months Ended				6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	May 31, 2017 item
Gain (loss) on the sale of assets						$ (1,603)	$ 4	$ (36)
Gain on retirement of debt			$ 110	$ 38		(55)	148	23
Gain associated with insurance recoveries		$ 30
Midwater Floater asset group
Loss associated with impairment of assets held and used	$ 94					94		668
Deepwater Floater asset group
Loss associated with impairment of assets held and used		$ 52					52	$ 507
Assets held for sale
Aggregate loss on impairment of assets held for sale					$ 1,400		$ 41
Sale of high specification jackups \| Assets sold, not discontinued operations
Gain (loss) on the sale of assets	$ 1,600					$ (1,600)
Number of High-Specification Jackups (in drilling units) \| item	10								10
Number of High-Specification Jackup under construction (in drilling units) \| item	5								5

Subsequent Events (Details) NOK / shares in Units, $ / shares in Units, shares in Millions, $ in Millions				3 Months Ended
	Jan. 30, 2018 USD ($) $ / shares shares	Aug. 13, 2017 NOK item NOK / shares shares	Aug. 13, 2017 item NOK / shares $ / shares	Mar. 31, 2018 USD ($) shares
Subsequent events
Number of new directors \| item		1
Songa
Subsequent events
Ratio of shares to be issued for consideration		0.3572
Business combination consideration (per share) \| NOK / shares		NOK 47.50	NOK 47.50
Maximum cash consideration per shareholder \| NOK		NOK 125,000
Number of Harsh Environment Floaters \| item		4	4
Songa \| Subsequent Event
Subsequent events
Business combination consideration (per share) \| $ / shares	$ 10.99
Newly issued shares (in shares) \| shares	66.9
Ownership interest (as a percent)	97.70%
Newly issued shares market value	$ 735
Exchangeable Bonds \| Songa
Subsequent events
Debt issued in acquisition (in dollars per share) \| $ / shares			NOK 2.99726
Debt instrument interest rate stated percentage		0.50%	0.50%
Exchangeable Bonds \| Songa \| Subsequent Event
Subsequent events
Convertible debt	$ 854
Debt conversion ratio	97.29756
Debt conversion (in dollars per share) \| $ / shares	$ 10.28
Maximum \| Songa
Subsequent events
Newly issued shares (in shares) \| shares		68.6
Maximum \| Songa \| Subsequent Event
Subsequent events
Cash payment	$ 1
Forecast \| Songa \| Subsequent Event
Subsequent events
Newly issued shares (in shares) \| shares				1.6
Forecast \| Exchangeable Bonds \| Songa \| Subsequent Event
Subsequent events
Convertible debt				$ 13

Schedule II - Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful accounts receivable
Reserves and allowances deducted from asset accounts
Balance at the beginning of the period			$ 14
Charge to cost and expenses	$ 0	$ 0	0
Deductions			14
Allowance for obsolete materials and supplies
Reserves and allowances deducted from asset accounts
Balance at the beginning of the period	153	148	109
Charge to cost and expenses	24	15	62
Deductions	36	10	23
Balance at the end of the period	141	153	148
Valuation allowance on deferred tax assets
Reserves and allowances deducted from asset accounts
Balance at the beginning of the period	412	380	409
Charge to cost and expenses	162	32	10
Deductions			39
Balance at the end of the period	$ 574	$ 412	$ 380