Quarterly report pursuant to Section 13 or 15(d)

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

v3.21.1
Funds Held for Clients and Corporate Investments (Narrative) (Details)
$ in Millions
9 Months Ended
Feb. 28, 2021
USD ($)
security
Feb. 28, 2021
USD ($)
security
May 31, 2020
USD ($)
security
Schedule of Available-for-sale Securities [Line Items]      
Net unrealized gains on available-for-sale securities $ 82.1 $ 82.1 $ 100.0
Number of available-for-sale securities in an unrealized loss position | security 163 163 19
Percentage of available-for-sale securities in an unrealized loss position 13.00% 13.00% 2.00%
Gross unrealized losses on available-for-sale securities $ 4.4 $ 4.4 $ 1.7
Corporate Bonds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Gross unrealized losses on available-for-sale securities $ 0.2 0.2 0.1
Corporate Bonds [Member] | Minimum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities maturity date Mar. 01, 2021    
Corporate Bonds [Member] | Maximum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities maturity date Feb. 08, 2028    
Municipal Bonds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Gross unrealized losses on available-for-sale securities $ 2.9 $ 2.9 $ 1.6
Municipal Bonds [Member] | Minimum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities maturity date Mar. 01, 2021    
Municipal Bonds [Member] | Maximum [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Available-for-sale securities maturity date Mar. 01, 2028    
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