Stockholders' Equity - Fair Value of Awards Granted and Vested (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]
Fair value of restricted shares granted	$ 53	$ 44	$ 36
Fair value of restricted shares vested	21	18	47
RSAs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted shares granted	33	28	20
Fair value of restricted shares vested	19	15	23
PSAs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted shares vested	0	3	15
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted shares granted	20	16	16
Fair value of restricted shares vested	$ 2	$ 0	$ 9