Quarterly report [Sections 13 or 15(d)]

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

v3.25.4
Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details) - USD ($)
$ in Millions
Nov. 30, 2025
May 31, 2025
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses $ (5.2) $ (3.0)
Securities in an unrealized loss position for less than twelve months, Fair value 486.2 300.1
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (36.9) (65.0)
Securities in an unrealized loss position for more than twelve months, Fair value 1,411.2 1,651.4
Total, Gross unrealized losses (42.1) (68.0)
Total, Fair value 1,897.4 1,951.5
Asset-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses 0.0 0.0
Securities in an unrealized loss position for less than twelve months, Fair value   16.4
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses 0.0 0.0
Securities in an unrealized loss position for more than twelve months, Fair value 2.8 2.8
Total, Gross unrealized losses 0.0 0.0
Total, Fair value 2.8 19.2
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 (0.6) (0.1)
Securities in an unrealized loss position for less than twelve months, Fair value 198.7 83.2
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (3.6) (6.9)
Securities in an unrealized loss position for more than twelve months, Fair value 183.7 236.7
Total, Gross unrealized losses (4.2) (7.0)
Total, Fair value 382.4 319.9
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 (2.1) (2.2)
Securities in an unrealized loss position for less than twelve months, Fair value 44.8 48.5
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (24.6) (42.1)
Securities in an unrealized loss position for more than twelve months, Fair value 825.7 880.1
Total, Gross unrealized losses (26.7) (44.3)
Total, Fair value 870.5 928.6
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 (2.5) (0.7)
Securities in an unrealized loss position for less than twelve months, Fair value 242.7 152.0
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (8.7) (16.0)
Securities in an unrealized loss position for more than twelve months, Fair value 399.0 531.8
Total, Gross unrealized losses (11.2) (16.7)
Total, Fair value $ 641.7 $ 683.8