Quarterly report pursuant to Section 13 or 15(d)

Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details)

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Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Feb. 28, 2022
USD ($)
Item
Feb. 28, 2021
USD ($)
Item
Feb. 28, 2022
USD ($)
Segment
Item
Feb. 28, 2021
USD ($)
Item
May 31, 2022
USD ($)
May 31, 2021
USD ($)
Item
Accounting Policies [Line Items]            
Number of reportable segments | Segment     1      
Allowance for credit losses $ 17.8   $ 17.8     $ 16.0
Advance collections 1.6   1.6     2.5
Maximum individual health insurance claims liability           0.3
Stock-based compensation costs recognized $ 12.8 $ 12.6 $ 39.2 $ 38.1    
ASU No. 2020-08 [Member]            
Accounting Policies [Line Items]            
Change in accounting principle, accounting standards update, adoption date Jun. 01, 2021   Jun. 01, 2021      
Change in accounting principle, accounting standards update, adopted [true false] true   true      
Change in accounting principle, accounting standards update, immaterial effect [true false] true   true      
ASU No. 2019-12 [Member]            
Accounting Policies [Line Items]            
Change in accounting principle, accounting standards update, adoption date Jun. 01, 2021   Jun. 01, 2021      
Change in accounting principle, accounting standards update, adopted [true false] true   true      
Change in accounting principle, accounting standards update, immaterial effect [true false] true   true      
Forecast [Member]            
Accounting Policies [Line Items]            
Maximum individual health insurance claims liability         $ 0.5  
Trade Receivables [Member]            
Accounting Policies [Line Items]            
Receivables $ 120.2   $ 120.2     98.4
Purchased Receivables [Member]            
Accounting Policies [Line Items]            
Receivables $ 618.5   $ 618.5     $ 495.9
Accounts And Unbilled Receivables [Member]            
Accounting Policies [Line Items]            
Number of clients creating a credit concentration | Item     0     0
Revenue [Member]            
Accounting Policies [Line Items]            
Number of clients creating a credit concentration | Item 0 0 0 0    
PEO [Member]            
Accounting Policies [Line Items]            
Maximum individual workers' compensation claims liability           $ 1.0
PEO [Member] | Forecast [Member]            
Accounting Policies [Line Items]            
Individual workers' compensation claims liability         1.0  
PEO Aggregate Claims Exceeding $1.0M [Member] | Minimum [Member] | Forecast [Member]            
Accounting Policies [Line Items]            
Individual workers' compensation claims liability         1.0  
PEO Aggregate Claims Exceeding $1.0M [Member] | Maximum [Member] | Forecast [Member]            
Accounting Policies [Line Items]            
Maximum individual workers' compensation claims liability         $ 2.0