Income Taxes - Tax Cuts and Jobs Act ("Act") (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes.
Statutory U.S. Federal tax rate (as a percent)	21.00%	21.00%	21.00%	35.00%
Provisional amount expected to be offset by available foreign tax credits			$ 314	$ 331
Provisional amount expected to be offset by available foreign tax credits primarily attributable to state taxes			2	2
Provisional amount expected to be offset by available foreign tax credits primarily attributable to state taxes recognized as a reduction of income tax expense from continuing operations			2
Adjustment of provisional amount of transition tax			17
Change to income tax expense due to impact of foreign tax credits			0
Provisional amount recorded related to the remeasurement of the net deferred tax assets			2	162
Provisional offset amount recorded related to the remeasurement of the net deferred tax assets			$ (2)	(162)
Benefit for the reduction of a deferred tax liability related to an indefinite lived intangible asset				$ 11