Quarterly report pursuant to Section 13 or 15(d)

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

v3.6.0.2
Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details) - USD ($)
$ in Millions
Nov. 30, 2016
May 31, 2016
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses $ (31.4) $ (0.5)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (0.1) (0.2)
Total, Gross unrealized losses (31.5) (0.7)
Securities in an unrealized loss position for less than twelve months, Fair value 1,933.2 141.1
Securities in an unrealized loss position for more than twelve months, Fair value 3.7 14.5
Total, Fair value 1,936.9 155.6
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 (1.3) (0.1)
Total, Gross unrealized losses (1.3) (0.1)
Securities in an unrealized loss position for less than twelve months, Fair value 67.8 14.7
Total, Fair value 67.8 14.7
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 (14.3) (0.1)
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (0.1)  
Total, Gross unrealized losses (14.4) (0.1)
Securities in an unrealized loss position for less than twelve months, Fair value 981.2 48.9
Securities in an unrealized loss position for more than twelve months, Fair value 2.7 2.8
Total, Fair value 983.9 51.7
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 15.3 5.7
Total, Fair value 15.3 5.7
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 (10.5)  
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses   (0.2)
Total, Gross unrealized losses (10.5) (0.2)
Securities in an unrealized loss position for less than twelve months, Fair value 654.7 20.7
Securities in an unrealized loss position for more than twelve months, Fair value 1.0 11.7
Total, Fair value 655.7 32.4
U.S. Government Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses (5.3) (0.3)
Total, Gross unrealized losses (5.3) (0.3)
Securities in an unrealized loss position for less than twelve months, Fair value 214.2 51.1
Total, Fair value $ 214.2 $ 51.1