Quarterly report pursuant to Section 13 or 15(d)

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

v3.20.1
Funds Held for Clients and Corporate Investments (Narrative) (Details)
$ in Millions
 9 Months Ended
Feb. 29, 2020
USD ($)
security
May 31, 2019
USD ($)
security
Schedule of Available-for-sale Securities [Line Items]    
Net unrealized gains on available-for-sale securities | $ $ 84.1 $ 19.7
Number of available-for-sale securities in an unrealized loss position | security 2 269
Number of available-for-sale securities in an unrealized loss position for more than twelve months | security 2  
Securities in an unrealized loss position for more than twelve months, fair value | $ $ 1.4 $ 558.5
Number of available-for-sale securities in an unrealized loss position for less than twelve months | security 0  
U.S. Government Agency And Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for more than twelve months, fair value | $   $ 175.6
Available-for-sale securities contractual maturities 90 days  
Variable Rate Demand Notes [Member] | Minimum [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities contractual maturities 20 years  
Variable Rate Demand Notes [Member] | Maximum [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities contractual maturities 30 years