Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Funds Held for Clients and Corporate Investments (Narrative) (Details)
$ in Millions
3 Months Ended 9 Months Ended
Feb. 28, 2019
USD ($)
security
Feb. 28, 2018
USD ($)
Feb. 28, 2019
USD ($)
security
Feb. 28, 2018
USD ($)
May 31, 2018
USD ($)
security
Schedule of Available-for-sale Securities [Line Items]          
Net unrealized losses on available-for-sale securities $ 9.8   $ 9.8   $ 38.3
Number of available-for-sale securities in an unrealized loss position | security 667   667   970
Gross unrealized losses on available-for-sale securities $ 17.8   $ 17.8   $ 40.7
Realized gains (losses) on available-for-sale securities $ 0.4 $ (0.2) $ 0.5 $ (0.6)  
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