Quarterly report pursuant to Section 13 or 15(d)

Service Revenue (Summary of PEO Pass-Through Costs Netted in Revenue) (Details)

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Service Revenue (Summary of PEO Pass-Through Costs Netted in Revenue) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Feb. 28, 2021
Feb. 29, 2020
Feb. 28, 2021
Feb. 29, 2020
Service Revenue [Abstract]        
Payroll wages and payroll taxes $ 5,500.0 $ 5,600.0 $ 15,500.0 $ 15,900.0
State unemployment insurance (included in payroll wages and payroll taxes) 73.1 47.2 98.7 73.9
Guaranteed cost benefit plans $ 146.1 $ 159.0 $ 439.6 $ 489.8