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 6 Months Ended
Nov. 30, 2020
Nov. 30, 2019
Nov. 30, 2020
Nov. 30, 2019
Service Revenue [Abstract]        
Payroll wages and payroll taxes $ 5,100.0 $ 5,200.0 $ 10,000.0 $ 10,300.0
State unemployment insurance (included in payroll wages and payroll taxes) 12.8 12.0 25.6 26.7
Guaranteed cost benefit plans $ 143.1 $ 165.0 $ 293.5 $ 330.8