Quarterly report pursuant to Section 13 or 15(d)

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

v3.19.1
Funds Held for Clients and Corporate Investments (Funds Held for Clients and Corporate Investments) (Details) - USD ($)
$ in Millions
Feb. 28, 2019
May 31, 2018
Schedule of Available-for-sale Securities [Line Items]    
Funds held for clients' money market securities and other cash equivalents, Amortized cost $ 2,874.7 $ 1,942.3
Funds held for clients' money market securities and other cash equivalents, Gross unrealized gains  
Funds held for clients' money market securities and other cash equivalents, Gross unrealized losses  
Funds held for clients' money market securities and other cash equivalents, Fair value 2,874.7 1,942.3
Available-for-sale securities, Amortized cost 2,567.1 3,143.1
Available-for-sale securities, Gross unrealized gains 8.0 2.4
Available-for-sale securities, Gross unrealized losses (17.8) (40.7)
Available-for-sale securities, Fair value 2,557.3 3,104.8
Other, Amortized cost 27.3 16.1
Other, Gross unrealized gains 2.0 2.1
Other, Gross unrealized losses (0.2)
Other, Fair value 29.1 18.2
Total funds held for clients and corporate investments, Amortized cost 5,469.1 5,101.5
Total funds held for clients and corporate investments, Gross unrealized gains 10.0 4.5
Total funds held for clients and corporate investments, Gross unrealized losses (18.0) (40.7)
Total funds held for clients and corporate investments, Fair value 5,461.1 5,065.3
Corporate Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 410.9  
Available-for-sale securities, Gross unrealized gains 1.5  
Available-for-sale securities, Gross unrealized losses (4.3)  
Available-for-sale securities, Fair value 408.1  
General Obligation Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 870.1 1,231.6
Available-for-sale securities, Gross unrealized gains 3.6 1.3
Available-for-sale securities, Gross unrealized losses (2.6) (11.2)
Available-for-sale securities, Fair value 871.1 1,221.7
Pre-Refunded Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost [1] 47.8 50.9
Available-for-sale securities, Gross unrealized gains [1] 0.2 0.1
Available-for-sale securities, Gross unrealized losses [1]   (0.1)
Available-for-sale securities, Fair value [1] 48.0 50.9
Revenue Municipal Bonds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 562.7 813.5
Available-for-sale securities, Gross unrealized gains 2.1 0.9
Available-for-sale securities, Gross unrealized losses (1.9) (8.0)
Available-for-sale securities, Fair value 562.9 806.4
U.S. Government Agency Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 493.7 410.2
Available-for-sale securities, Gross unrealized gains 0.6
Available-for-sale securities, Gross unrealized losses (9.0) (14.1)
Available-for-sale securities, Fair value 485.3 396.1
Variable Rate Demand Notes [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Available-for-sale securities, Amortized cost 181.9 308.3
Available-for-sale securities, Gross unrealized gains  
Available-for-sale securities, Gross unrealized losses  
Available-for-sale securities, Fair value $ 181.9 $ 308.3
[1] Pre-refunded municipal bonds are secured by an escrow fund of U.S. government obligations.