Financial Instruments - Fair Values on Recurring Basis (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Equity Securities, FV-NI, Unrealized Gain (Loss)	$ (31)
Recurring
Schedule of Investments [Line Items]
Cash	8,363	$ 9,776
Total Estimated Fair Value
Cash, cash equivalents and marketable securities	49,599	55,342
Less: Restricted cash, cash equivalents, and marketable securities	(307)	(321)
Total cash, cash equivalents, and marketable securities	49,292	55,021
Cost or Amortized Cost
Cash, cash equivalents and marketable securities	49,585
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax
Debt Securities, Available for Sale, Unrealized Gain	97
Debt Securities, Available for Sale, Unrealized Loss	(259)
Recurring \| Level 1 securities
Total Estimated Fair Value
Equity Securities, FV-NI	174	202
Recurring \| Level 1 securities \| Money market funds
Schedule of Investments [Line Items]
Money market funds	16,260	18,850
Recurring \| Level 2 securities
Total Estimated Fair Value
Equity Securities, FV-NI	2	5
Recurring \| Level 2 securities \| Foreign government and agency securities
Total Estimated Fair Value
Debt Securities, Available for Sale, Fair Value	3,466	4,794
Cost or Amortized Cost
Debt Securities, Available for Sale, Cost	3,467
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax
Debt Securities, Available for Sale, Unrealized Gain	0
Debt Securities, Available for Sale, Unrealized Loss	(1)
Recurring \| Level 2 securities \| U.S. government and agency securities
Total Estimated Fair Value
Debt Securities, Available for Sale, Fair Value	4,345	7,080
Cost or Amortized Cost
Debt Securities, Available for Sale, Cost	4,295
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax
Debt Securities, Available for Sale, Unrealized Gain	51
Debt Securities, Available for Sale, Unrealized Loss	(1)
Recurring \| Level 2 securities \| Corporate debt securities
Total Estimated Fair Value
Debt Securities, Available for Sale, Fair Value	13,793	11,881
Cost or Amortized Cost
Debt Securities, Available for Sale, Cost	13,957
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax
Debt Securities, Available for Sale, Unrealized Gain	41
Debt Securities, Available for Sale, Unrealized Loss	(205)
Recurring \| Level 2 securities \| Asset-backed securities
Total Estimated Fair Value
Debt Securities, Available for Sale, Fair Value	2,820	2,360
Cost or Amortized Cost
Debt Securities, Available for Sale, Cost	2,868
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax
Debt Securities, Available for Sale, Unrealized Gain	3
Debt Securities, Available for Sale, Unrealized Loss	(51)
Recurring \| Level 2 securities \| Other fixed income securities
Total Estimated Fair Value
Debt Securities, Available for Sale, Fair Value	376	$ 394
Cost or Amortized Cost
Debt Securities, Available for Sale, Cost	375
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax
Debt Securities, Available for Sale, Unrealized Gain	2
Debt Securities, Available for Sale, Unrealized Loss	(1)
Money market funds \| Recurring \| Level 1 securities \| Money market funds
Schedule of Investments [Line Items]
Money market funds	$ 16,260

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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 of 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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