Restructuring and Integration - Summary of Restructuring Costs (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	$ 6
Inception to Date	111
Estimated Remaining Costs	29
Estimated Total Cost	140	[1]
Employer Solutions
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	5
Inception to Date	96
Estimated Remaining Costs	25
Estimated Total Cost	121	[1]
Employer Solutions | Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	2
Inception to Date	48
Estimated Remaining Costs	11
Estimated Total Cost	59	[1]
Employer Solutions | Other Restructuring Costs
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	3	[2]
Inception to Date	48	[2]
Estimated Remaining Costs	14	[2]
Estimated Total Cost	62	[1],[2]
Professional Services
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	1
Inception to Date	15
Estimated Remaining Costs	4
Estimated Total Cost	19	[1]
Professional Services | Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Inception to Date	8
Estimated Remaining Costs	2
Estimated Total Cost	10	[1]
Professional Services | Other Restructuring Costs
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	1	[2]
Inception to Date	7	[2]
Estimated Remaining Costs	2	[2]
Estimated Total Cost	$ 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.