Significant Accounting Policies	12 Months Ended
Dec. 31, 2019
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 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, allowance for excess and obsolete materials and supplies, property and equipment, assets held for sale, goodwill, income taxes, contingencies, share-based compensation and 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 a valuation requires multiple input levels, 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 unconsolidated 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—Unconsolidated Affiliates and Note 16—Equity. Business combinations—We apply the acquisition method of accounting for business combinations, under which we record the acquired assets and assumed liabilities at fair value and recognize goodwill to the extent the consideration transferred exceeds the fair value of the net assets acquired. To the extent the fair value of the net assets acquired exceeds the consideration transferred, we recognize a bargain purchase gain. We estimate the fair values of the acquired assets and assumed liabilities as of the date of the acquisition, and our estimates are subject to adjustment through completion, which is in each case within one year of the acquisition date, based on our ongoing assessments of the fair values of property and equipment, intangible assets, other assets and liabilities and our evaluation of tax positions and contingencies. See Note 4—Business Combinations. Goodwill—We conduct impairment testing for our goodwill annually as of October 1 and more frequently, on an interim basis, when an event occurs or circumstances change that indicate that the fair value of our reporting unit may have declined below its carrying value. We test 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 have a single reporting unit for this purpose. Before testing goodwill, we consider whether or not to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If, as the result of our qualitative assessment, we determine that an impairment test is required, or, alternatively, if we elect to forgo the qualitative assessment, we record an impairment to goodwill to the extent the carrying amount of the reporting unit, including goodwill, exceeds the fair value of the reporting unit. In the year ended December 31, 2018, as a result of an interim goodwill test, we recognized an aggregate loss of $462 million, which had no tax effect, associated with the impairment of our goodwill. See Note 4—Business Combinations and Note 8—Goodwill and Other Intangibles. Contract intangibles—We recognize contract intangible assets and liabilities related to acquired executory contracts, such as drilling contracts and construction contracts. The drilling contract intangible assets represent the amount by which the fixed dayrates of the acquired contracts were above the market dayrates that were available or expected to be available during the term of the contract for similar contracts, measured as of the acquisition date. We amortize the carrying amount of the drilling contract intangible assets using the straight-line method over the expected remaining contract period as a reduction of contract drilling revenues. At December 31, 2019 and 2018, the aggregate carrying amount of our drilling contract intangible assets was $608 million and $795 million, respectively. The construction contract intangible liabilities represent the amount by which the remaining payments due under the acquired contracts were above market construction rates for similar drilling units, measured as of the acquisition date. Upon cancellation of the construction contracts, we eliminated the contract intangible liabilities with a corresponding adjustment to earnings. See Note 4—Business Combinations and Note 8—Goodwill and Other Intangibles. Derivative instruments—We record derivatives on our consolidated balance sheet, measured at fair value. We recognize the gains and losses associated with changes in the fair value of undesignated derivatives in current period earnings. See Note 11—Derivative Instruments. Revenue recognition—We recognize revenues earned under our drilling contracts based on variable dayrates, which range from a full operating dayrate to lower rates or zero rates for periods when drilling operations are interrupted or restricted, based on the specific activities we perform during the contract on an hourly, or more frequent, basis. Such dayrate consideration is attributed to the distinct time period to which it relates within the contract term, and therefore, is recognized as we perform the services. When the operating dayrate declines over the contract term, we recognize revenues on a straight-line basis over the full contract period. We recognize reimbursement revenues and the corresponding costs as we provide the customer-requested goods and services, when such reimbursable costs are incurred while performing drilling operations. Prior to performing drilling operations, we may receive pre-operating revenues, on either a fixed lump-sum or variable dayrate basis, for mobilization, contract preparation, customer-requested goods and services or capital upgrades, which we recognize on a straight-line basis over the estimated contract period. We recognize losses for loss contracts as such losses are incurred. We recognize revenues for demobilization over the contract period unless otherwise constrained. We recognize revenues from contract terminations as we fulfill our obligations and all contingencies have been resolved. To obtain contracts with our customers, we incur costs to prepare a rig for contract and mobilize a rig to the drilling location. We defer pre-operating costs, such as contract preparation and mobilization costs, and recognize such costs on a straight-line basis, consistent with the general pace of activity, in operating and maintenance costs over the estimated contract period. We apply the optional exemption that permits us to exclude disclosure of the estimated transaction price related to the variable portion of unsatisfied performance obligations at the end of the reporting period, as our transaction price is based on a single performance obligation consisting of a series of distinct hourly, or more frequent, periods, the variability of which will be resolved at the time of the future services. See Note 6—Revenues. Share-based compensation—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 granted or modified stock options, we use the Black-Scholes-Merton option-pricing model and apply assumptions for the expected life, risk-free interest rate, expected volatility and dividend yield. To measure the fair values of granted or modified performance-based restricted share units 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 use 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 such 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. See Note 17—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. In the years ended December 31, 2019, 2018 and 2017, we capitalized interest costs of $38 million, $37 million and $116 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, 2019, 2018 and 2017, we recognized a net gain of $2 million, a net loss of $38 million and a net loss of $6 million, respectively, related to currency exchange rates. Income taxes—We provide for income taxes based on the tax laws and rates in effect in the countries in which we operate and earn income. We recognize the effect of changes in tax laws as of the date of enactment. We recognize potential global intangible low-taxed income inclusions as a period cost. 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 12—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 with high credit ratings. Accounts receivable—We earn our revenues by providing our drilling services to integrated oil companies, government-owned or government-controlled oil companies and other independent 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. See Note 3—Accounting Standards Updates. Materials and supplies—We record materials and supplies at their average cost less an allowance for excess and obsolete items. We estimate the allowance for excess and obsolete items based on historical experience and expectations for future use of the materials and supplies. At December 31, 2019 and 2018, our allowance for excess and obsolete items was $127 million and $134 million, respectively. Restricted cash accounts and investments—We maintain restricted cash accounts 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 accounts and investments in current assets if the restriction is expected to expire or otherwise be resolved within one year or if such funds are considered to offset liabilities that are properly classified as current liabilities. At December 31, 2019, the aggregate carrying amount of our restricted cash accounts and investments was $558 million, recorded in current assets. At December 31, 2018, the aggregate carrying amount of our restricted cash accounts and investments was $552 million, of which $551 million and $1 million was classified in current assets and other assets, respectively. See Note 10—Debt, Note 15—Commitments and Contingencies and Note 20—Financial Instruments. 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, 2019, we had no assets classified as held for sale. At December 31, 2018, the aggregate carrying amount of our assets held for sale, recorded in other current assets, was $25 million. See Note 7—Drilling Fleet. Property and equipment—The recognition of our property and equipment, consisting primarily of offshore drilling rigs and related equipment, requires us to apply judgment related to estimates and assumptions for cost capitalization, useful lives and salvage values of our rigs. These estimates and assumptions are based on both historical experience and expectations regarding future industry conditions and operations. At December 31, 2019, 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 30 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, including property and equipment and right-of-use assets, 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 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. See Note 7—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. We calculate investment gains or losses for this purpose 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, the most significant of which include long-term rate of return on plan assets, discount rates and mortality rates. 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. At December 31, 2019 and 2018, our pension and other postemployment benefit plan obligations represented an aggregate liability of $351 million and $362 million, respectively, and an aggregate asset of $42 million and $47 million, respectively, representing the funded status of the plans. In the years ended December 31, 2019, 2018 and 2017, aggregate net periodic benefit costs were income of $3 million, income of $9 million and costs of $5 million, respectively. See Note 14—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.

Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Note 2—Significant Accounting Policies

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, allowance for excess and obsolete materials and supplies, property and equipment, assets held for sale, goodwill, income taxes, contingencies, share-based compensation and 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 a valuation requires multiple input levels, 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 unconsolidated 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—Unconsolidated Affiliates and Note 16—Equity.

Business combinations—We apply the acquisition method of accounting for business combinations, under which we record the acquired assets and assumed liabilities at fair value and recognize goodwill to the extent the consideration transferred exceeds the fair value of the net assets acquired. To the extent the fair value of the net assets acquired exceeds the consideration transferred, we recognize a bargain purchase gain. We estimate the fair values of the acquired assets and assumed liabilities as of the date of the acquisition, and our estimates are subject to adjustment through completion, which is in each case within one year of the acquisition date, based on our ongoing assessments of the fair values of property and equipment, intangible assets, other assets and liabilities and our evaluation of tax positions and contingencies. See Note 4—Business Combinations.

Goodwill—We conduct impairment testing for our goodwill annually as of October 1 and more frequently, on an interim basis, when an event occurs or circumstances change that indicate that the fair value of our reporting unit may have declined below its carrying value. We test 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 have a single reporting unit for this purpose. Before testing goodwill, we consider whether or not to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If, as the result of our qualitative assessment, we determine that an impairment test is required, or, alternatively, if we elect to forgo the qualitative assessment, we record an impairment to goodwill to the extent the carrying amount of the reporting unit, including goodwill, exceeds the fair value of the reporting unit. In the year ended December 31, 2018, as a result of an interim goodwill test, we recognized an aggregate loss of $462 million, which had no tax effect, associated with the impairment of our goodwill. See Note 4—Business Combinations and Note 8—Goodwill and Other Intangibles.

Contract intangibles—We recognize contract intangible assets and liabilities related to acquired executory contracts, such as drilling contracts and construction contracts. The drilling contract intangible assets represent the amount by which the fixed dayrates of the acquired contracts were above the market dayrates that were available or expected to be available during the term of the contract for similar contracts, measured as of the acquisition date. We amortize the carrying amount of the drilling contract intangible assets using the straight-line method over the expected remaining contract period as a reduction of contract drilling revenues. At December 31, 2019 and 2018, the aggregate carrying amount of our drilling contract intangible assets was $608 million and $795 million, respectively. The construction contract intangible liabilities represent the amount by which the remaining payments due under the acquired contracts were above market construction rates for similar drilling units, measured as of the acquisition date. Upon cancellation of the construction contracts, we eliminated the contract intangible liabilities with a corresponding adjustment to earnings. See Note 4—Business Combinations and Note 8—Goodwill and Other Intangibles.

Derivative instruments—We record derivatives on our consolidated balance sheet, measured at fair value. We recognize the gains and losses associated with changes in the fair value of undesignated derivatives in current period earnings. See Note 11—Derivative Instruments.

Revenue recognition—We recognize revenues earned under our drilling contracts based on variable dayrates, which range from a full operating dayrate to lower rates or zero rates for periods when drilling operations are interrupted or restricted, based on the specific activities we perform during the contract on an hourly, or more frequent, basis. Such dayrate consideration is attributed to the distinct time period to which it relates within the contract term, and therefore, is recognized as we perform the services. When the operating dayrate declines over the contract term, we recognize revenues on a straight-line basis over the full contract period. We recognize reimbursement revenues and the corresponding costs as we provide the customer-requested goods and services, when such reimbursable costs are incurred while performing drilling operations. Prior to performing drilling operations, we may receive pre-operating revenues, on either a fixed lump-sum or variable dayrate basis, for mobilization, contract preparation, customer-requested goods and services or capital upgrades, which we recognize on a straight-line basis over the estimated contract period. We recognize losses for loss contracts as such losses are incurred. We recognize revenues for demobilization over the contract period unless otherwise constrained. We recognize revenues from contract terminations as we fulfill our obligations and all contingencies have been resolved. To obtain contracts with our customers, we incur costs to prepare a rig for contract and mobilize a rig to the drilling location. We defer pre-operating costs, such as contract preparation and mobilization costs, and recognize such costs on a straight-line basis, consistent with the general pace of activity, in operating and maintenance costs over the estimated contract period. We apply the optional exemption that permits us to exclude disclosure of the estimated transaction price related to the variable portion of unsatisfied performance obligations at the end of the reporting period, as our transaction price is based on a single performance obligation consisting of a series of distinct hourly, or more frequent, periods, the variability of which will be resolved at the time of the future services. See Note 6—Revenues.

Share-based compensation—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 granted or modified stock options, we use the Black-Scholes-Merton option-pricing model and apply assumptions for the expected life, risk-free interest rate, expected volatility and dividend yield. To measure the fair values of granted or modified performance-based restricted share units 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 use 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 such 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. See Note 17—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. In the years ended December 31, 2019, 2018 and 2017, we capitalized interest costs of $38 million, $37 million and $116 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, 2019, 2018 and 2017, we recognized a net gain of $2 million, a net loss of $38 million and a net loss of $6 million, respectively, related to currency exchange rates.

Income taxes—We provide for income taxes based on the tax laws and rates in effect in the countries in which we operate and earn income. We recognize the effect of changes in tax laws as of the date of enactment. We recognize potential global intangible low-taxed income inclusions as a period cost. 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 12—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 with high credit ratings.

Accounts receivable—We earn our revenues by providing our drilling services to integrated oil companies, government-owned or government-controlled oil companies and other independent 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. See Note 3—Accounting Standards Updates.

Materials and supplies—We record materials and supplies at their average cost less an allowance for excess and obsolete items. We estimate the allowance for excess and obsolete items based on historical experience and expectations for future use of the materials and supplies. At December 31, 2019 and 2018, our allowance for excess and obsolete items was $127 million and $134 million, respectively.

Restricted cash accounts and investments—We maintain restricted cash accounts 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 accounts and investments in current assets if the restriction is expected to expire or otherwise be resolved within one year or if such funds are considered to offset liabilities that are properly classified as current liabilities. At December 31, 2019, the aggregate carrying amount of our restricted cash accounts and investments was $558 million, recorded in current assets. At December 31, 2018, the aggregate carrying amount of our restricted cash accounts and investments was $552 million, of which $551 million and $1 million was classified in current assets and other assets, respectively. See Note 10—Debt, Note 15—Commitments and Contingencies and Note 20—Financial Instruments.

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, 2019, we had no assets classified as held for sale. At December 31, 2018, the aggregate carrying amount of our assets held for sale, recorded in other current assets, was $25 million. See Note 7—Drilling Fleet.

Property and equipment—The recognition of our property and equipment, consisting primarily of offshore drilling rigs and related equipment, requires us to apply judgment related to estimates and assumptions for cost capitalization, useful lives and salvage values of our rigs. These estimates and assumptions are based on both historical experience and expectations regarding future industry conditions and operations. At December 31, 2019, 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 30 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, including property and equipment and right-of-use assets, 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 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. See Note 7—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. We calculate investment gains or losses for this purpose 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, the most significant of which include long-term rate of return on plan assets, discount rates and mortality rates. 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.

At December 31, 2019 and 2018, our pension and other postemployment benefit plan obligations represented an aggregate liability of $351 million and $362 million, respectively, and an aggregate asset of $42 million and $47 million, respectively, representing the funded status of the plans. In the years ended December 31, 2019, 2018 and 2017, aggregate net periodic benefit costs were income of $3 million, income of $9 million and costs of $5 million, respectively. See Note 14—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.