Segment Reporting - Schedule of Current Reportable Segments by Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 690	$ 668	$ 1,361	$ 2,008
Employer Solutions
Segment Reporting Information [Line Items]
Revenue	587	559	1,156	1,678
Employer Solutions | Recurring
Segment Reporting Information [Line Items]
Revenue	522	498	1,049	1,516
Employer Solutions | Project
Segment Reporting Information [Line Items]
Revenue	65	61	107	162
Professional Services
Segment Reporting Information [Line Items]
Revenue	93	93	184	272
Professional Services | Recurring
Segment Reporting Information [Line Items]
Revenue	32	28	60	78
Professional Services | Project
Segment Reporting Information [Line Items]
Revenue	61	65	124	194
Hosted Business
Segment Reporting Information [Line Items]
Revenue	$ 10	$ 16	$ 21	$ 58