Financial Instruments - Fair Values on Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Equity Securities, FV-NI, Gain (Loss) [Abstract]
Equity securities, unrealized gain (loss)	$ 448
Recurring
Schedule of Investments [Line Items]
Cash	10,063	$ 9,776
Cost or Amortized Cost
Cash, cash equivalents and short-term investments	83,624	55,083
Gross Unrealized Gains
Short-term investments	377	55
Gross Unrealized Losses
Cash equivalents and marketable securities	(5)	(3)
Total Estimated Fair Value
Cash, cash equivalents and short-term investments	84,653	55,342
Less: Restricted cash, cash equivalents, and marketable securities	(257)	(321)
Total cash, cash equivalents, and marketable securities	84,396	55,021
Recurring | Level 1 securities
Total Estimated Fair Value
Equity securities	617	202
Recurring | Level 1 securities | Money market funds
Schedule of Investments [Line Items]
Money market funds	27,430	18,850
Recurring | Level 1 securities | Money market funds | Money market funds
Schedule of Investments [Line Items]
Money market funds	27,430
Recurring | Level 2 securities
Total Estimated Fair Value
Equity securities	40	5
Recurring | Level 2 securities | Foreign government and agency securities
Cost or Amortized Cost
Cash equivalents and marketable securities	5,130	4,794
Gross Unrealized Gains
Cash equivalents and marketable securities	1	0
Gross Unrealized Losses
Cash equivalents and marketable securities	0	0
Total Estimated Fair Value
Cash equivalents and marketable securities	5,131	4,794
Recurring | Level 2 securities | U.S. government and agency securities
Cost or Amortized Cost
Cash equivalents and marketable securities	7,410	7,070
Gross Unrealized Gains
Cash equivalents and marketable securities	30	11
Gross Unrealized Losses
Cash equivalents and marketable securities	(1)	(1)
Total Estimated Fair Value
Cash equivalents and marketable securities	7,439	7,080
Recurring | Level 2 securities | Corporate debt securities
Cost or Amortized Cost
Cash equivalents and marketable securities	29,684	11,845
Gross Unrealized Gains
Cash equivalents and marketable securities	305	37
Gross Unrealized Losses
Cash equivalents and marketable securities	(1)	(1)
Total Estimated Fair Value
Cash equivalents and marketable securities	29,988	11,881
Recurring | Level 2 securities | Asset-backed securities
Cost or Amortized Cost
Cash equivalents and marketable securities	3,206	2,355
Gross Unrealized Gains
Cash equivalents and marketable securities	32	6
Gross Unrealized Losses
Cash equivalents and marketable securities	(3)	(1)
Total Estimated Fair Value
Cash equivalents and marketable securities	3,235	2,360
Recurring | Level 2 securities | Other fixed income securities
Cost or Amortized Cost
Cash equivalents and marketable securities	701	393
Gross Unrealized Gains
Cash equivalents and marketable securities	9	1
Gross Unrealized Losses
Cash equivalents and marketable securities	0	0
Total Estimated Fair Value
Cash equivalents and marketable securities	$ 710	$ 394