Financial Instruments - Fair Values on Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Equity Securities Gains	$ 4
Recurring
Schedule of Investments [Line Items]
Cash	9,776	$ 10,406
Cost or Amortized Cost
Cash, cash equivalents and short-term investments	55,083	41,516
Gross Unrealized Gains
Short-term investments	55	2
Gross Unrealized Losses
Cash equivalents and marketable securities	(3)	(45)
Total Estimated Fair Value
Cash, cash equivalents and short-term investments	55,342	41,676
Less: Restricted cash, cash equivalents, and marketable securities	(321)	(426)
Total cash, cash equivalents, and marketable securities	55,021	41,250
Recurring \| Level 1 securities
Total Estimated Fair Value
Equity securities	202	170
Recurring \| Level 1 securities \| Money market funds
Schedule of Investments [Line Items]
Money market funds	18,850	12,515
Recurring \| Level 1 securities \| Money market funds \| Money market funds
Schedule of Investments [Line Items]
Money market funds	18,850
Recurring \| Level 2 securities
Total Estimated Fair Value
Equity securities	5	33
Recurring \| Level 2 securities \| Foreign government and agency securities
Cost or Amortized Cost
Cash equivalents and marketable securities	4,794	815
Gross Unrealized Gains
Cash equivalents and marketable securities	0	0
Gross Unrealized Losses
Cash equivalents and marketable securities	0	0
Total Estimated Fair Value
Cash equivalents and marketable securities	4,794	815
Recurring \| Level 2 securities \| U.S. government and agency securities
Cost or Amortized Cost
Cash equivalents and marketable securities	7,070	11,686
Gross Unrealized Gains
Cash equivalents and marketable securities	11	1
Gross Unrealized Losses
Cash equivalents and marketable securities	(1)	(20)
Total Estimated Fair Value
Cash equivalents and marketable securities	7,080	11,667
Recurring \| Level 2 securities \| Corporate debt securities
Cost or Amortized Cost
Cash equivalents and marketable securities	11,845	5,008
Gross Unrealized Gains
Cash equivalents and marketable securities	37	1
Gross Unrealized Losses
Cash equivalents and marketable securities	(1)	(19)
Total Estimated Fair Value
Cash equivalents and marketable securities	11,881	4,990
Recurring \| Level 2 securities \| Asset-backed securities
Cost or Amortized Cost
Cash equivalents and marketable securities	2,355	896
Gross Unrealized Gains
Cash equivalents and marketable securities	6	0
Gross Unrealized Losses
Cash equivalents and marketable securities	(1)	(4)
Total Estimated Fair Value
Cash equivalents and marketable securities	2,360	892
Recurring \| Level 2 securities \| Other fixed income securities
Cost or Amortized Cost
Cash equivalents and marketable securities	393	190
Gross Unrealized Gains
Cash equivalents and marketable securities	1	0
Gross Unrealized Losses
Cash equivalents and marketable securities	0	(2)
Total Estimated Fair Value
Cash equivalents and marketable securities	$ 394	$ 188

Cash, Cash Equivalents And Debt Available-For-Sale Securities, Amortized Cost Basis [Abstract]

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Equity Securities, FV-NI, and Debt Securities, Available-for-sale-Accumulated Gross Unrealized Gain, before tax Amount of unrealized gain on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI) and amount, before tax, of unrealized gain on debt securities in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Amount of unrealized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Cash and investments whose use in whole or in part is restricted for the long-term, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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