Quarterly report pursuant to Section 13 or 15(d)

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

v3.20.1
Funds Held for Clients and Corporate Investments (Funds Held for Clients and Corporate Investments) (Details) - USD ($)
$ in Millions
Feb. 29, 2020
May 31, 2019
Schedule of Available-for-sale Securities [Line Items]    
Funds held for clients' money market securities and other cash equivalents, Amortized cost $ 1,226.1 $ 204.5
Funds held for clients' money market securities and other cash equivalents, Fair value 1,226.1 204.5
Available-for-sale securities, Amortized cost 3,102.3 3,601.1
Available-for-sale securities, Gross unrealized gains 84.1 22.4
Available-for-sale securities, Gross unrealized losses   (2.7)
Available-for-sale securities, Fair value 3,186.4 3,620.8
Other, Amortized cost 25.6 26.3
Other, Gross unrealized gains 2.0 1.7
Other, Gross unrealized losses (0.4) (0.3)
Other, Fair value 27.2 27.7
Total funds held for clients and corporate investments, Amortized cost 4,354.0 3,831.9
Total funds held for clients and corporate investments, Gross unrealized gains 86.1 24.1
Total funds held for clients and corporate investments, Gross unrealized losses (0.4) (3.0)
Total funds held for clients and corporate investments, Fair value 4,439.7 3,853.0
Asset-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 68.0 5.3
Available-for-sale securities, Gross unrealized gains 1.1  
Available-for-sale securities, Fair value 69.1 5.3
Corporate Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 667.6 442.1
Available-for-sale securities, Gross unrealized gains 24.0 5.3
Available-for-sale securities, Gross unrealized losses   (0.9)
Available-for-sale securities, Fair value 691.6 446.5
General Obligation Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 741.8 840.6
Available-for-sale securities, Gross unrealized gains 16.9 7.5
Available-for-sale securities, Gross unrealized losses   (0.3)
Available-for-sale securities, Fair value 758.7 847.8
Pre-Refunded Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost [1] 21.9 25.6
Available-for-sale securities, Gross unrealized gains [1] 0.3 0.2
Available-for-sale securities, Fair value [1] 22.2 25.8
Revenue Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 586.9 545.4
Available-for-sale securities, Gross unrealized gains 14.5 4.7
Available-for-sale securities, Gross unrealized losses   (0.2)
Available-for-sale securities, Fair value 601.4 549.9
U.S. Government Agency And Treasury Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 866.2 612.5
Available-for-sale securities, Gross unrealized gains 27.3 4.7
Available-for-sale securities, Gross unrealized losses   (1.3)
Available-for-sale securities, Fair value 893.5 615.9
Variable Rate Demand Notes [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 149.9 1,129.6
Available-for-sale securities, Fair value $ 149.9 $ 1,129.6
[1] Pre-refunded municipal bonds are secured by an escrow fund of U.S. government obligations.