Restructuring and Integration - Summary of Restructuring Costs (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($)		Jun. 30, 2022 USD ($)
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	$ 14		$ 20
Inception to Date	125		125
Estimated Remaining Costs	15		15
Estimated Total Cost	140	[1]	140	[1]
Employer Solutions
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	13		18
Inception to Date	109		109
Estimated Remaining Costs	12		12
Estimated Total Cost	121	[1]	121	[1]
Employer Solutions | Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	3		5
Inception to Date	51		51
Estimated Remaining Costs	8		8
Estimated Total Cost	59	[1]	59	[1]
Employer Solutions | Other Restructuring Costs
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	10	[2]	13	[2]
Inception to Date	58	[2]	58	[2]
Estimated Remaining Costs	4	[2]	4	[2]
Estimated Total Cost	62	[1],[2]	62	[1],[2]
Professional Services
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	1		2
Inception to Date	16		16
Estimated Remaining Costs	3		3
Estimated Total Cost	19	[1]	19	[1]
Professional Services | Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Inception to Date	8		8
Estimated Remaining Costs	2		2
Estimated Total Cost	10	[1]	10	[1]
Professional Services | Other Restructuring Costs
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	1	[2]	2	[2]
Inception to Date	8	[2]	8	[2]
Estimated Remaining Costs	1	[2]	1	[2]
Estimated Total Cost	$ 9	[1],[2]	$ 9	[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.