Annual report [Section 13 and 15(d), not S-K Item 405]

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

v3.25.2
Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details) - USD ($)
$ in Millions
May 31, 2025
May 31, 2024
Schedule of Available-for-sale Securities [Line Items]    
Securities in an unrealized loss position for less than twelve months, Gross unrealized losses $ (3.0) $ (23.0)
Securities in an unrealized loss position for less than twelve months, Fair value 300.1 1,068.9
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (65.0) (141.2)
Securities in an unrealized loss position for more than twelve months, Fair value 1,651.4 2,102.7
Total, Gross unrealized losses (68.0) (164.2)
Total, Fair value 1,951.5 3,171.6
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 (0.4)
Securities in an unrealized loss position for less than twelve months, Fair value 16.4 77.4
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses 0.0 (0.7)
Securities in an unrealized loss position for more than twelve months, Fair value 2.8 43.0
Total, Gross unrealized losses 0.0 (1.1)
Total, Fair value 19.2 120.4
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 (0.1) (8.4)
Securities in an unrealized loss position for less than twelve months, Fair value 83.2 620.8
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (6.9) (24.4)
Securities in an unrealized loss position for more than twelve months, Fair value 236.7 647.8
Total, Gross unrealized losses (7.0) (32.8)
Total, Fair value 319.9 1,268.6
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 (2.2) (8.0)
Securities in an unrealized loss position for less than twelve months, Fair value 48.5 102.5
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (42.1) (78.9)
Securities in an unrealized loss position for more than twelve months, Fair value 880.1 864.7
Total, Gross unrealized losses (44.3) (86.9)
Total, Fair value 928.6 967.2
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 (0.7) (6.2)
Securities in an unrealized loss position for less than twelve months, Fair value 152.0 268.2
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (16.0) (37.2)
Securities in an unrealized loss position for more than twelve months, Fair value 531.8 547.2
Total, Gross unrealized losses (16.7) (43.4)
Total, Fair value $ 683.8 $ 815.4