Quarterly report pursuant to Section 13 or 15(d)

Service Revenue (Narrative) (Details)

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Service Revenue (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Nov. 30, 2019
Nov. 30, 2018
Nov. 30, 2019
Nov. 30, 2018
Service Revenue [Line Items]        
Contracts term     30 days  
Notice of termination period     30 days  
Direct pass-through costs for payroll wages and payroll taxes $ 5,200.0 $ 2,300.0 $ 10,300.0 $ 4,500.0
Direct pass-through costs related to state unemployment insurance 12.0 4.6 26.7 13.4
Direct pass-through costs related to guaranteed cost benefit plans $ 165.0 $ 80.4 $ 330.8 155.1
Revenue performance obligations timing     the Company defers revenue associated with these performance obligations, which exceed one year, and subsequently recognizes these as future services are provided, over approximately three years to four years  
Capitalized contract cost, amortization period 8 years   8 years  
Impairment loss     $ 0.0 $ 0.0
Minimum [Member]        
Service Revenue [Line Items]        
Revenue performance obligations timing, years     3 years  
Maximum [Member]        
Service Revenue [Line Items]        
Revenue performance obligations timing, years     4 years