Service Revenue (Summary of PEO Pass-Through Costs Netted in Revenue) (Details) - USD ($) $ in Millions  | 
12 Months Ended | ||
|---|---|---|---|
May 31, 2024  | 
May 31, 2023  | 
May 31, 2022  | 
|
| Revenue from Contract with Customer [Abstract] | |||
| Payroll wages and payroll taxes | $ 27,381.5 | $ 26,025.3 | $ 24,209.3 | 
| State unemployment insurance (included in payroll wages and payroll taxes) | 151.8 | 138.2 | 139.1 | 
| Guaranteed cost benefit plans | $ 660.3 | $ 656.3 | $ 641.4 | 
| X | ||||||||||
- Definition Direct Pass Through Cost Guaranteed Cost Benefit Plans No definition available. 
  | 
| X | ||||||||||
- Definition Direct Pass Through Cost Payroll Wages And Taxes Including Federal And State Unemployment Insurance No definition available. 
  | 
| X | ||||||||||
- Definition Direct Pass Through Cost State Unemployment Insurance No definition available. 
  | 
| X | ||||||||||
- References No definition available. 
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