Annual report pursuant to Section 13 and 15(d)

Funds Held for Clients and Corporate Investments (Classification of Investments on Consolidated Balance Sheets) (Details)

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Funds Held for Clients and Corporate Investments (Classification of Investments on Consolidated Balance Sheets) (Details) - USD ($)
$ in Millions
May 31, 2017
May 31, 2016
Funds Held for Clients and Corporate Investments [Abstract]    
Funds held for clients $ 4,301.9 $ 3,997.5
Corporate investments 138.8 220.6
Long-term corporate investments 454.0 441.1
Total funds held for clients and corporate investments, Fair value $ 4,894.7 $ 4,659.2