Stockholders' Equity - Fair Value of Awards Granted and Vested (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total granted	$ 55	$ 48
Total vested	20	18
RSAs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total granted	36	30
Total vested	19	16
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total granted	19	18
Total vested	$ 1	$ 2