Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.3
Funds Held for Clients and Corporate Investments (Narrative) (Details)
$ in Millions
 3 Months Ended
Aug. 31, 2019
USD ($)
security
May 31, 2019
USD ($)
security
Schedule of Available-for-sale Securities [Line Items]    
Net unrealized gains on available-for-sale securities $ 53.4 $ 19.7
Number of available-for-sale securities in an unrealized loss position | security 74 269
Gross unrealized losses on available-for-sale securities $ 0.5 $ 2.7
U.S. Government Agency And Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Gross unrealized losses on available-for-sale securities $ 0.4 $ 1.3
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