Annual report [Section 13 and 15(d), not S-K Item 405]

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

v3.25.2
Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details)
 12 Months Ended
May 31, 2025
USD ($)
Item
Segment
May 31, 2024
USD ($)
Item
May 31, 2023
USD ($)
Item
Accounting Policies [Line Items]      
Number of reportable segments | Segment 1    
Cash and cash equivalents $ 1,628,600,000 $ 1,468,900,000 $ 1,222,000,000
Advance collections 1,800,000 700,000  
Goodwill, impairment loss 0 0 0
Impairment of intangible assets with indefinite useful lives 0 0 0
Impairment of long-lived assets 0 0 0
Realized gains or losses from foreign exchange transactions 0 0 0
Impairment loss, assets recognized from the costs to obtain and fufill contracts 0 0 0
Workers' compensation insurance costs in current liabilities 80,400,000 74,100,000  
Workers' compensation insurance costs in long-term liabilities 156,400,000 144,500,000  
Maximum individual health insurance claims liability 500,000 500,000  
PEO accrued health insurance and dental and vision plan reserves in current liabilities 48,200,000 50,600,000  
Operating lease, impairment loss $ 0 $ 0 $ 0
Change in accounting principle, accounting standards update, adopted [true false] true    
Change in accounting principle, accounting standards update, immaterial effect [true false] true    
Accounting Standards Update [Extensible Enumeration] us-gaap:AccountingStandardsUpdate202307Member    
Minimum [Member]      
Accounting Policies [Line Items]      
Payroll funding fees average collection period 35 days    
Processing fee average collection period 5 days    
Minimum [Member] | Software [Member]      
Accounting Policies [Line Items]      
Estimated useful lives 3 years    
Minimum [Member] | Software Development [Member]      
Accounting Policies [Line Items]      
Estimated useful lives 12 years    
Maximum [Member]      
Accounting Policies [Line Items]      
Payroll funding fees average collection period 50 days    
Processing fee average collection period 15 days    
Maximum [Member] | Software [Member]      
Accounting Policies [Line Items]      
Estimated useful lives 5 years    
Revenue [Member]      
Accounting Policies [Line Items]      
Number of clients creating a credit concentration | Item 0 0 0
Accounts And Unbilled Receivables [Member]      
Accounting Policies [Line Items]      
Number of clients creating a credit concentration | Item 0 0  
PEO Aggregate Claims Exceeding $1.0M [Member] | Minimum [Member]      
Accounting Policies [Line Items]      
Individual workers' compensation claims liability $ 1,000,000 $ 1,000,000  
PEO Aggregate Claims Exceeding $1.0M [Member] | Maximum [Member]      
Accounting Policies [Line Items]      
Maximum individual workers' compensation claims liability 1,000,000 1,000,000  
PEO And Insurance Solutions [Member]      
Accounting Policies [Line Items]      
Cash and cash equivalents $ 179,800,000 $ 171,700,000