Restructuring and Integration - Summary of Restructuring Costs (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($)		Sep. 30, 2022 USD ($)
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	$ 23		$ 43
Inception to Date	148		148
Estimated Remaining Costs	7		7
Estimated Total Cost	155	[1]	155	[1]
Employer Solutions
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	16		34
Inception to Date	125		125
Estimated Remaining Costs	5		5
Estimated Total Cost	130	[1]	130	[1]
Employer Solutions | Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	4		9
Inception to Date	55		55
Estimated Remaining Costs	3		3
Estimated Total Cost	58	[1]	58	[1]
Employer Solutions | Other Restructuring Costs
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	12	[2]	25	[2]
Inception to Date	70	[2]	70	[2]
Estimated Remaining Costs	2	[2]	2	[2]
Estimated Total Cost	72	[1],[2]	72	[1],[2]
Professional Services
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	7		9
Inception to Date	23		23
Estimated Remaining Costs	2		2
Estimated Total Cost	25	[1]	25	[1]
Professional Services | Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	1		1
Inception to Date	9		9
Estimated Remaining Costs	1		1
Estimated Total Cost	10	[1]	10	[1]
Professional Services | Other Restructuring Costs
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	6	[2]	8	[2]
Inception to Date	14	[2]	14	[2]
Estimated Remaining Costs	1	[2]	1	[2]
Estimated Total Cost	$ 15	[1],[2]	$ 15	[1],[2]

[1] Actual costs, when incurred, may vary due to changes in the assumptions built into the Plan. Significant assumptions that may change when plans are finalized and implemented include, but are not limited to, changes in severance calculations, changes in the assumptions underlying sublease loss calculations due to changing market conditions, and changes in the overall analysis that might cause the Company to add or cancel component initiatives.

[2] Other costs associated with the Plan primarily include consulting and legal fees and lease consolidation.