Annual report pursuant to Section 13 and 15(d)

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

v3.20.2
Funds Held for Clients and Corporate Investments (Narrative) (Details)
$ in Millions
 12 Months Ended
May 31, 2020
USD ($)
security
May 31, 2019
USD ($)
security
Schedule of Available-for-sale Securities [Line Items]    
Net unrealized gains on available-for-sale securities $ 100.0 $ 19.7
Number of available-for-sale securities in an unrealized loss position | security 19 269
Percentage of available-for-sale securities in an unrealized loss position 2.00% 28.00%
Gross unrealized losses on available-for-sale securities $ 1.7 $ 2.7
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