Income Taxes - Deferred Income Tax Valuation Allowance Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets Valuation Allowance [Roll Forward]
Beginning balance of deferred income tax valuation allowance	$ 126	$ 122	$ 72
Increases charged to income tax expense	0	0	28
Charges against goodwill	0	15	22
Decreases	(7)	(11)	0
Ending balance of deferred income tax valuation allowance	$ 119	$ 126	$ 122