Restructuring - Summary of Restructuring Costs (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
Restructuring Cost And Reserve [Line Items]
Restructuring Costs		$ 15	$ 23
Inception to Date		88
Estimated Remaining Costs		34
Estimated Total Cost		122
Employer Solutions
Restructuring Cost And Reserve [Line Items]
Restructuring Costs		13	17
Inception to Date		69
Estimated Remaining Costs		29
Estimated Total Cost		98
Employer Solutions | Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Restructuring Costs		2
Inception to Date		7
Estimated Remaining Costs		5
Estimated Total Cost		12
Employer Solutions | Other Restructuring Costs
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	[1]	11	17
Inception to Date	[1]	62
Estimated Remaining Costs	[1]	24
Estimated Total Cost	[1]	86
Corporate
Restructuring Cost And Reserve [Line Items]
Restructuring Costs		2	6
Inception to Date		19
Estimated Remaining Costs		5
Estimated Total Cost		24
Corporate | Severance and Related Benefits
Restructuring Cost And Reserve [Line Items]
Restructuring Costs		2	5
Inception to Date		17
Estimated Remaining Costs		4
Estimated Total Cost		21
Corporate | Other Restructuring Costs
Restructuring Cost And Reserve [Line Items]
Restructuring Costs	[1]		$ 1
Inception to Date	[1]	2
Estimated Remaining Costs	[1]	1
Estimated Total Cost	[1]	$ 3

[1] Other restructuring costs associated with the Transformation Program primarily include data center exit costs, third party fees associated with the restructuring, and costs associated with transitioning existing technology and processes.