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Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended			6 Months Ended
Fair Value Measurements - Narrative (Details) - USD ($)	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 23, 2021	Jan. 14, 2021	Dec. 31, 2020	Apr. 06, 2020	Oct. 31, 2018
Derivative [Line Items]
Accumulated other comprehensive loss	$ 1,510,000,000			$ 1,510,000,000				$ 1,581,000,000
Other current and long-term liabilities	(47,000,000)	$ (2,190,000,000)		(264,000,000)	$ (2,111,000,000)
Net cash related to derivative contracts under collateral exchange arrangements	0	(1,212,000,000)	$ 580,000,000	0	(632,000,000)
Level 3 \| Fair Value
Derivative [Line Items]
Carrying amounts of deferred purchase price assets	770,000,000			770,000,000				884,000,000
Interest Expense
Derivative [Line Items]
Amount amortized from AOCI into interest expense	47,000,000	39,000,000		93,000,000	39,000,000
Amount expected to be amortized from AOCI into interest expense over next 12 months				196,000,000
Senior Secured Notes due 2025, 3.500%
Derivative [Line Items]
Interest rate, stated percentage									3.50%
Senior Secured Notes due 2050, 4.500%
Derivative [Line Items]
Interest rate, stated percentage									4.50%
Senior Notes
Derivative [Line Items]
Principal Issuances						$ 3,800,000,000	$ 3,000,000,000.0		$ 19,000,000,000.0
Interest Rate Contract
Derivative [Line Items]
Accumulated other comprehensive loss	$ 1,500,000,000			$ 1,500,000,000				$ 1,600,000,000
Derivative liabilities		2,300,000,000			2,300,000,000
Cash-collateralized		$ 1,200,000,000			1,200,000,000
Other current and long-term liabilities					2,300,000,000
Net cash related to derivative contracts under collateral exchange arrangements					$ 1,200,000,000
Interest Rate Contract \| Cash Flow Hedging
Derivative [Line Items]
Aggregate notional amount										$ 9,600,000,000