Stockholders' Equity - Components of Share-based Compensation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax Charges	$ 39	$ 27	$ 46
Net-of-Tax Amount	37	26	40
Restructuring settled without cash			23
RSAs, PSAs and PSUs (defined below)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax Charges	29	17	39
Net-of-Tax Amount	28	17	35
Employee stock purchase plan and stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax Charges	10	10	7
Net-of-Tax Amount	$ 9	$ 9	$ 5