Service Revenue (Summary of PEO Pass-Through Costs Netted in Revenue) (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Aug. 31, 2026 |
Aug. 31, 2025 |
|
| Revenue from Contract with Customer [Abstract] | ||
| Payroll wages and payroll taxes | $ 8,713.5 | $ 7,356.1 |
| State unemployment insurance (included in payroll wages and payroll taxes) | 27.7 | 23.7 |
| Guaranteed cost benefit plans | $ 214.4 | $ 175.5 |