Stock-Based Compensation - Expense for performance based shares units (Details) - Performance Shares - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award
Share-based payment arrangement, expense	$ 0	$ 1	$ 3	$ 3
Total Stockholder Return
Share-based Compensation Arrangement by Share-based Payment Award
Share-based payment arrangement, expense	2	0	3	3
Relative Revenue Growth
Share-based Compensation Arrangement by Share-based Payment Award
Share-based payment arrangement, expense	(3)	1	(1)	0
Adjusted Earnings Per Share
Share-based Compensation Arrangement by Share-based Payment Award
Share-based payment arrangement, expense	$ 1	$ 0	$ 1	$ 0