Income Taxes - Change in Deferred Tax Asset Valuation Allowance (Details) - Valuation Allowance of Deferred Tax Assets - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 93	$ 83	$ 68
Additions	0	29	15
Reductions/ Charges	(20)	(19)	0
Balance at End of Year	$ 73	$ 93	$ 83