Quarterly report [Sections 13 or 15(d)]

Funds Held for Clients and Corporate Investments (Funds Held for Clients and Corporate Investments) (Details)

v3.25.4
Funds Held for Clients and Corporate Investments (Funds Held for Clients and Corporate Investments) (Details) - USD ($)
$ in Millions
Nov. 30, 2025
May 31, 2025
Schedule of Available-for-sale Securities [Line Items]    
Funds held for clients' money market securities and other restricted cash equivalents, Amortized cost $ 337.1 $ 1,057.8
Funds held for clients' money market securities and other restricted cash equivalents, Fair value 337.1 1,057.8
AFS securities, Amortized cost 4,547.6 3,809.1
AFS securities, Gross unrealized gains 33.1 14.4
AFS securities, Gross unrealized losses (42.1) (68.0)
AFS securities, Fair value 4,538.6 3,755.5
Other, Amortized cost 33.6 33.1
Other, Gross unrealized gains 4.5 2.3
Other, Gross unrealized losses (0.5) (0.9)
Other, Fair value 37.6 34.5
Total funds held for clients and corporate investments, Amortized cost 4,918.3 4,900.0
Total funds held for clients and corporate investments, Gross unrealized gains 37.6 16.7
Total funds held for clients and corporate investments, Gross unrealized losses (42.6) (68.9)
Total funds held for clients and corporate investments, Fair value 4,913.3 4,847.8
Asset-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
AFS securities, Amortized cost 141.4 158.3
AFS securities, Gross unrealized gains 1.3 0.9
AFS securities, Gross unrealized losses 0.0 0.0
AFS securities, Fair value 142.7 159.2
Corporate Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
AFS securities, Amortized cost 2,283.3 1,640.3
AFS securities, Gross unrealized gains 22.2 10.7
AFS securities, Gross unrealized losses (4.2) (7.0)
AFS securities, Fair value 2,301.3 1,644.0
Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
AFS securities, Amortized cost 950.8 1,017.3
AFS securities, Gross unrealized gains 1.2 0.5
AFS securities, Gross unrealized losses (26.7) (44.3)
AFS securities, Fair value 925.3 973.5
U.S. Government Agency And Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
AFS securities, Amortized cost 1,172.1 993.2
AFS securities, Gross unrealized gains 8.4 2.3
AFS securities, Gross unrealized losses (11.2) (16.7)
AFS securities, Fair value $ 1,169.3 $ 978.8