Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2016
Significant Accounting Policies
Accounting estimates	Accounting estimates—To prepare financial statements in accordance with accounting principles generally accepted in the 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 plans and other postretirement benefits. 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 5—Variable Interest Entities and Note 14—Noncontrolling Interest.
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, 2016, 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 20 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.
Discontinued operations	Discontinued operations—Under accounting standards previously in effect, we presented as discontinued operations the operating results of components of our business that either had been disposed of or were classified as held for sale when both of the following conditions were met: (a) the operations and cash flows of the component had been or would be eliminated from our ongoing operations as a result of the disposal transaction and (b) we would not have any significant continuing involvement in the operations of the disposed component. Under the former accounting standards, we considered a component of our business to be one that comprises operations and cash flows that could be clearly distinguished, operationally and for financial reporting purposes, from the rest of our business. See Note 3—New Accounting Pronouncements and Note 8—Discontinued Operations.
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.
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—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. We recognize share‑based compensation expense net of a forfeiture rate that we estimate at the time of grant based on historical experience and future expectations, and we adjust the estimated forfeiture rate, if necessary, in subsequent periods based on actual forfeitures or changed expectations. 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. We recognize cash flows resulting from the tax deduction benefits for awards in excess of recognized compensation costs as financing cash flows. In the years ended December 31, 2016, 2015 and 2014, share‑based compensation expense was $42 million, $64 million and $98 million, respectively. In the years ended December 31, 2016, 2015 and 2014, income tax benefit on share‑based compensation expense was $7 million, $11 million and $15 million, respectively. See Note 16—Share Based Compensation Plans.
Capitalized interest	Capitalized interest—We capitalize interest costs for qualifying construction and upgrade projects and only capitalize interest during periods in which progress for the construction projects continues to be underway. In the years ended December 31, 2016, 2015 and 2014, we capitalized interest costs of $176 million, $140 million and $133 million, respectively, for our construction work in progress.
Foreign currency	Foreign 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, 2016, 2015 and 2014, we recognized a net loss of $2 million, a net gain of less than $1 million and a net gain of $18 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. 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 recognize deferred tax assets and liabilities for the anticipated future tax effects of temporary differences between the financial statement basis and the tax basis of our assets and liabilities using the applicable jurisdictional tax rates in effect at year end. 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 7—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. 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 other 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, 2016, the aggregate carrying amount of our restricted cash investments was $510 million, of which $466 million and $44 million was classified in other current assets and other assets, respectively. At December 31, 2015, the aggregate carrying amount of our restricted cash investments was $467 million, of which $340 million and $127 million was classified in other current assets and other assets, respectively. See Note 11—Debt and Note 13—Commitments and Contingencies.
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, 2016 and 2015, 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, 2016 and 2015, the allowance for obsolescence was $153 million and $148 million, respectively.
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, 2016 and 2015, the aggregate carrying amount of our assets held for sale, recorded in other current assets, was $6 million and $8 million, respectively. See Note 10—Drilling Fleet.
Long-lived assets and definite-lived intangible assets	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, midwater floaters and high‑specification jackups. 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, 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) 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. In the year ended December 31, 2014, we determined that the carrying amount of the deepwater floater asset group exceeded its fair value, and we recognized a loss of $788 million ($693 million, or $1.91 per diluted share, net of tax) associated with the impairment of these long‑lived assets. 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 6—Impairments.
Goodwill impairment	Goodwill impairment—Prior to the full impairment of our goodwill, we conducted impairment testing annually as of October 1 and more frequently, on an interim basis, when an event occured or circumstances changed that indicated that the fair value of our reporting unit may have declined below its carrying value. We tested goodwill at the reporting unit level, which is defined as an operating segment or one level below an operating segment that constitutes a business for which financial information is available and is regularly reviewed by management. We determined that we had a single reporting unit for this purpose. We estimate the fair value of our reporting unit using projected discounted cash flows, publicly traded company multiples and acquisition multiples. To develop the projected cash flows associated with our reporting unit, which are based on estimated future dayrates and rig utilization, we consider key factors that include assumptions regarding future commodity prices, credit market conditions and the effect these factors may have on our contract drilling operations and the capital expenditure budgets of our customers. We discount the projected cash flows using a long‑term, risk‑adjusted weighted‑average cost of capital, which is based on our estimate of the investment returns that market participants would require for each of our reporting units. We derive publicly traded company multiples for companies with operations similar to our reporting units using observable information related to shares traded on stock exchanges and, when available, observable information related to recent acquisitions. If the reporting unit’s carrying amount exceeds its fair value, we consider goodwill impaired and perform a second step to measure the amount of the impairment loss, if any. In the year ended December 31, 2014, as a result of interim goodwill tests, we recognized an aggregate loss of $3.0 billion, which had no tax effect, associated with the full impairment of the carrying amount of our goodwill, of which $2.9 billion ($8.02 per diluted share) was attributable to controlling interest and $74 million was attributable to noncontrolling interest. See Note
Pension and other postretirement benefits	Pension and other postretirement benefits—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 postretirement 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. Since our defined benefit plans 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, 2016 and 2015, our pension and other postretirement benefit plan obligations represented an aggregate liability of $375 million and $414 million, respectively, and an aggregate asset of $5 million and $2 million, respectively, representing the funded status of the plans. In the years ended December 31, 2016, 2015 and 2014, net periodic benefit costs were income of $11 million, costs of $26 million and costs of $75 million, respectively. See Note 12—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. These reclassifications did not have a material effect on our consolidated statement of financial position, results of operations or cash flows.

Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2016

Accounting estimates—To prepare financial statements in accordance with accounting principles generally accepted in the 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 plans and other postretirement benefits. 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 5—Variable Interest Entities and Note 14—Noncontrolling Interest.

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, 2016, 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 20 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.

Discontinued operations

Discontinued operations—Under accounting standards previously in effect, we presented as discontinued operations the operating results of components of our business that either had been disposed of or were classified as held for sale when both of the following conditions were met: (a) the operations and cash flows of the component had been or would be eliminated from our ongoing operations as a result of the disposal transaction and (b) we would not have any significant continuing involvement in the operations of the disposed component. Under the former accounting standards, we considered a component of our business to be one that comprises operations and cash flows that could be clearly distinguished, operationally and for financial reporting purposes, from the rest of our business. See Note 3—New Accounting Pronouncements and Note 8—Discontinued Operations.

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.

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—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. We recognize share‑based compensation expense net of a forfeiture rate that we estimate at the time of grant based on historical experience and future expectations, and we adjust the estimated forfeiture rate, if necessary, in subsequent periods based on actual forfeitures or changed expectations.

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. We recognize cash flows resulting from the tax deduction benefits for awards in excess of recognized compensation costs as financing cash flows. In the years ended December 31, 2016, 2015 and 2014, share‑based compensation expense was $42 million, $64 million and $98 million, respectively. In the years ended December 31, 2016, 2015 and 2014, income tax benefit on share‑based compensation expense was $7 million, $11 million and $15 million, respectively. See Note 16—Share Based Compensation Plans.

Capitalized interest

Capitalized interest—We capitalize interest costs for qualifying construction and upgrade projects and only capitalize interest during periods in which progress for the construction projects continues to be underway. In the years ended December 31, 2016, 2015 and 2014, we capitalized interest costs of $176 million, $140 million and $133 million, respectively, for our construction work in progress.

Foreign currency

Foreign 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, 2016, 2015 and 2014, we recognized a net loss of $2 million, a net gain of less than $1 million and a net gain of $18 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. 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 recognize deferred tax assets and liabilities for the anticipated future tax effects of temporary differences between the financial statement basis and the tax basis of our assets and liabilities using the applicable jurisdictional tax rates in effect at year end. 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 7—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.

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 other 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, 2016, the aggregate carrying amount of our restricted cash investments was $510 million, of which $466 million and $44 million was classified in other current assets and other assets, respectively. At December 31, 2015, the aggregate carrying amount of our restricted cash investments was $467 million, of which $340 million and $127 million was classified in other current assets and other assets, respectively. See Note 11—Debt and Note 13—Commitments and Contingencies.

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, 2016 and 2015, 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, 2016 and 2015, the allowance for obsolescence was $153 million and $148 million, respectively.

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, 2016 and 2015, the aggregate carrying amount of our assets held for sale, recorded in other current assets, was $6 million and $8 million, respectively. See Note 10—Drilling Fleet.

Long-lived assets and definite-lived intangible assets

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, midwater floaters and high‑specification jackups. 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, 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) 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. In the year ended December 31, 2014, we determined that the carrying amount of the deepwater floater asset group exceeded its fair value, and we recognized a loss of $788 million ($693 million, or $1.91 per diluted share, net of tax) associated with the impairment of these long‑lived assets. 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 6—Impairments.

Goodwill impairment

Goodwill impairment—Prior to the full impairment of our goodwill, we conducted impairment testing annually as of October 1 and more frequently, on an interim basis, when an event occured or circumstances changed that indicated that the fair value of our reporting unit may have declined below its carrying value. We tested goodwill at the reporting unit level, which is defined as an operating segment or one level below an operating segment that constitutes a business for which financial information is available and is regularly reviewed by management. We determined that we had a single reporting unit for this purpose.

We estimate the fair value of our reporting unit using projected discounted cash flows, publicly traded company multiples and acquisition multiples. To develop the projected cash flows associated with our reporting unit, which are based on estimated future dayrates and rig utilization, we consider key factors that include assumptions regarding future commodity prices, credit market conditions and the effect these factors may have on our contract drilling operations and the capital expenditure budgets of our customers. We discount the projected cash flows using a long‑term, risk‑adjusted weighted‑average cost of capital, which is based on our estimate of the investment returns that market participants would require for each of our reporting units. We derive publicly traded company multiples for companies with operations similar to our reporting units using observable information related to shares traded on stock exchanges and, when available, observable information related to recent acquisitions. If the reporting unit’s carrying amount exceeds its fair value, we consider goodwill impaired and perform a second step to measure the amount of the impairment loss, if any.

In the year ended December 31, 2014, as a result of interim goodwill tests, we recognized an aggregate loss of $3.0 billion, which had no tax effect, associated with the full impairment of the carrying amount of our goodwill, of which $2.9 billion ($8.02 per diluted share) was attributable to controlling interest and $74 million was attributable to noncontrolling interest. See Note

Pension and other postretirement benefits

Pension and other postretirement benefits—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 postretirement 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. Since our defined benefit plans 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, 2016 and 2015, our pension and other postretirement benefit plan obligations represented an aggregate liability of $375 million and $414 million, respectively, and an aggregate asset of $5 million and $2 million, respectively, representing the funded status of the plans. In the years ended December 31, 2016, 2015 and 2014, net periodic benefit costs were income of $11 million, costs of $26 million and costs of $75 million, respectively. See Note 12—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. These reclassifications did not have a material effect on our consolidated statement of financial position, results of operations or cash flows.