Quarterly report pursuant to Section 13 or 15(d)

Funds Held for Clients and Corporate Investments (Narrative) (Details)

v3.20.4
Funds Held for Clients and Corporate Investments (Narrative) (Details)
$ in Millions
 6 Months Ended
Nov. 30, 2020
USD ($)
security
Nov. 30, 2020
USD ($)
security
May 31, 2020
USD ($)
security
Schedule of Available-for-sale Securities [Line Items]      
Net unrealized gains on available-for-sale securities $ 108.9 $ 108.9 $ 100.0
Number of available-for-sale securities in an unrealized loss position | security 25 25 19
Percentage of available-for-sale securities in an unrealized loss position 3.00% 3.00% 2.00%
Gross unrealized losses on available-for-sale securities $ 0.5 $ 0.5 $ 1.7
Corporate Bonds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Gross unrealized losses on available-for-sale securities     0.1
Corporate Bonds [Member] | Minimum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities maturity date Jan. 11, 2021    
Corporate Bonds [Member] | Maximum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities maturity date Sep. 11, 2026    
Municipal Bonds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Gross unrealized losses on available-for-sale securities $ 0.5 $ 0.5 $ 1.6
Municipal Bonds [Member] | Minimum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities maturity date Dec. 01, 2020    
Municipal Bonds [Member] | Maximum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities maturity date Nov. 15, 2027    
VRDNs [Member] | Minimum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities contractual maturities   20 years  
VRDNs [Member] | Maximum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities contractual maturities   30 years