Annual report pursuant to Section 13 and 15(d)

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

v3.19.2
Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details) - USD ($)
$ in Millions
May 31, 2019
May 31, 2018
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses   $ (27.5)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses $ (2.7) (13.2)
Total, Gross unrealized losses (2.7) (40.7)
Securities in an unrealized loss position for less than twelve months, Fair value 9.4 1,907.0
Securities in an unrealized loss position for more than twelve months, Fair value 558.5 331.3
Total, Fair value 567.9 2,238.3
Corporate Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses   (6.0)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (0.9) (1.3)
Total, Gross unrealized losses (0.9) (7.3)
Securities in an unrealized loss position for less than twelve months, Fair value 1.5 271.5
Securities in an unrealized loss position for more than twelve months, Fair value 133.8 34.6
Total, Fair value 135.3 306.1
General Obligation Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses   (8.7)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (0.3) (2.5)
Total, Gross unrealized losses (0.3) (11.2)
Securities in an unrealized loss position for less than twelve months, Fair value 3.0 856.4
Securities in an unrealized loss position for more than twelve months, Fair value 168.3 68.9
Total, Fair value 171.3 925.3
Pre-Refunded Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses   (0.1)
Total, Gross unrealized losses   (0.1)
Securities in an unrealized loss position for less than twelve months, Fair value 0.1 18.5
Securities in an unrealized loss position for more than twelve months, Fair value 1.6 0.5
Total, Fair value 1.7 19.0
Revenue Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses   (6.3)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (0.2) (1.7)
Total, Gross unrealized losses (0.2) (8.0)
Securities in an unrealized loss position for less than twelve months, Fair value 0.1 540.9
Securities in an unrealized loss position for more than twelve months, Fair value 79.2 50.9
Total, Fair value 79.3 591.8
U.S. Government Agency And Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses   (6.4)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (1.3) (7.7)
Total, Gross unrealized losses (1.3) (14.1)
Securities in an unrealized loss position for less than twelve months, Fair value 4.7 219.7
Securities in an unrealized loss position for more than twelve months, Fair value 175.6 176.4
Total, Fair value $ 180.3 $ 396.1