Income Taxes - Reconciliation of Change in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Gross Unrecognized Tax Benefits
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 431	$ 440	$ 86
Additions for tax positions related to the current year	33	23	28
Additions for tax positions related to prior years	3	12	402
Reductions for tax positions related to prior years due to IRS and other settlements	(16)	(44)	(76)
Ending balance	451	431	440
Portion of balance at December 31, that, if recognized, would impact the effective income tax rate	153
Accrued Interest and Penalties
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	31	35	29
Additions for tax positions related to the current year	0	17	0
Additions for tax positions related to prior years	21	4	25
Reductions for tax positions related to prior years due to IRS and other settlements	(6)	(25)	(19)
Ending balance	46	31	35
Portion of balance at December 31, that, if recognized, would impact the effective income tax rate	35
Gross Tax, Interest and Penalties
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	462	475	115
Additions for tax positions related to the current year	33	40	28
Additions for tax positions related to prior years	24	16	427
Reductions for tax positions related to prior years due to IRS and other settlements	(22)	(69)	(95)
Ending balance	497	$ 462	$ 475
Portion of balance at December 31, that, if recognized, would impact the effective income tax rate	$ 188