Quarterly report [Sections 13 or 15(d)]

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

v3.25.1
Funds Held for Clients and Corporate Investments (Securities in Unrealized Loss Position) (Details) - USD ($)
$ in Millions
Feb. 28, 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 $ (2.7) $ (23.0)
Securities in an unrealized loss position for less than twelve months, Fair value 360.1 1,068.9
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (76.4) (141.2)
Securities in an unrealized loss position for more than twelve months, Fair value 1,738.1 2,102.7
Total, Gross unrealized losses (79.1) (164.2)
Total, Fair value 2,098.2 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 3.0 77.4
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (0.1) (0.7)
Securities in an unrealized loss position for more than twelve months, Fair value 6.0 43.0
Total, Gross unrealized losses (0.1) (1.1)
Total, Fair value 9.0 120.4
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 (0.6) (8.4)
Securities in an unrealized loss position for less than twelve months, Fair value 249.2 620.8
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (8.3) (24.4)
Securities in an unrealized loss position for more than twelve months, Fair value 280.3 647.8
Total, Gross unrealized losses (8.9) (32.8)
Total, Fair value 529.5 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 (1.7) (8.0)
Securities in an unrealized loss position for less than twelve months, Fair value 29.5 102.5
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (49.0) (78.9)
Securities in an unrealized loss position for more than twelve months, Fair value 922.3 864.7
Total, Gross unrealized losses (50.7) (86.9)
Total, Fair value 951.8 967.2
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 (0.4) (6.2)
Securities in an unrealized loss position for less than twelve months, Fair value 78.4 268.2
Securities in an unrealized loss position for more than twelve months, Gross unrealized losses (19.0) (37.2)
Securities in an unrealized loss position for more than twelve months, Fair value 529.5 547.2
Total, Gross unrealized losses (19.4) (43.4)
Total, Fair value $ 607.9 $ 815.4