Quarterly report pursuant to Section 13 or 15(d)

Funds Held for Clients and Corporate Investments (Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity) (Details)

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Funds Held for Clients and Corporate Investments (Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity) (Details) - USD ($)
$ in Millions
Aug. 31, 2019
May 31, 2019
Funds Held for Clients and Corporate Investments [Abstract]    
Due in one year or less, Amortized cost $ 254.5  
Due after one year through three years, Amortized cost 832.9  
Due after three years through five years, Amortized cost 992.1  
Due after five years, Amortized cost 939.9  
Available-for-sale securities, Amortized cost 3,019.4 $ 3,601.1
Due in one year or less, Fair value 255.6  
Due after one year through three years, Fair value 843.9  
Due after three years through five years, Fair value 1,013.2  
Due after five years, Fair value 960.1  
Available-for-sale securities, Fair value $ 3,072.8 $ 3,620.8