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
Aug. 31, 2020
Aug. 31, 2019
Service Revenue [Abstract]    
Payroll wages and payroll taxes $ 4,900.0 $ 5,100.0
State unemployment insurance (included in payroll wages and payroll taxes) 12.8 14.7
Guaranteed cost benefit plans $ 150.4 $ 165.8