Quarterly report pursuant to Section 13 or 15(d)

Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details)

v3.19.3
Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details) - USD ($)
$ in Millions
Aug. 31, 2019
May 31, 2019
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses $ (0.5) $ (2.7)
Total, Gross unrealized losses (0.5) (2.7)
Securities in an unrealized loss position for less than twelve months, Fair value 57.5 9.4
Securities in an unrealized loss position for more than twelve months, Fair value 116.7 558.5
Total, Fair value 174.2 567.9
Corporate Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (0.1) (0.9)
Total, Gross unrealized losses (0.1) (0.9)
Securities in an unrealized loss position for less than twelve months, Fair value 2.2 1.5
Securities in an unrealized loss position for more than twelve months, Fair value 31.7 133.8
Total, Fair value 33.9 135.3
General Obligation Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses   (0.3)
Total, Gross unrealized losses   (0.3)
Securities in an unrealized loss position for less than twelve months, Fair value   3.0
Securities in an unrealized loss position for more than twelve months, Fair value 2.2 168.3
Total, Fair value 2.2 171.3
Pre-Refunded Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Fair value   0.1
Securities in an unrealized loss position for more than twelve months, Fair value   1.6
Total, Fair value   1.7
Revenue Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses   (0.2)
Total, Gross unrealized losses   (0.2)
Securities in an unrealized loss position for less than twelve months, Fair value 1.8 0.1
Securities in an unrealized loss position for more than twelve months, Fair value   79.2
Total, Fair value 1.8 79.3
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, Gross unrealized losses (0.4) (1.3)
Total, Gross unrealized losses (0.4) (1.3)
Securities in an unrealized loss position for less than twelve months, Fair value 53.5 4.7
Securities in an unrealized loss position for more than twelve months, Fair value 82.8 175.6
Total, Fair value $ 136.3 $ 180.3