Income Taxes - Tax Cuts and Jobs Act ("Act") (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Statutory U.S. Federal tax rate (as a percent)	21.00%	35.00%	35.00%
Provisional amount recorded related to the remeasurement of the net deferred tax assets		$ 162
Provisional offset amount recorded related to the remeasurement of the net deferred tax assets		(162)
Benefit for the reduction of a deferred tax liability related to an indefinite lived intangible asset		11
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
Change to income tax expense due to impact of foreign tax credits	0
Adjustment of provisional amount of transition tax	$ 17