Stock Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock based compensation expense	$ 13	$ 11	$ 37	$ 31
Total stock based compensation capitalized	0	0	1	1
Cost of providing services
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock based compensation expense	3	2	9	7
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock based compensation expense	1	2	5	5
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock based compensation expense	8	6	21	17
Systems development and programming costs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock based compensation expense	$ 1	$ 1	$ 2	$ 2