Income Taxes - Rollforward of Total Unrecognized Tax Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, beginning of period	$ 2,031	$ 1,595	$ 2,181
Tax Positions Related to Current Year: Additions	121	138	64
Tax Positions Related to Current Year: Reductions	0	0	0
Tax Positions Related to Prior Years: Additions	398	405	125
Tax Positions Related to Prior Years: Reductions	(481)	0	0
Settlements	(454)	(104)	(774)
Lapse of statute of limitations	(1)	(3)	(1)
Balance, end of period	$ 1,614	$ 2,031	$ 1,595

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of unrecognized tax benefits.

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Amount of decrease in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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