Annual report pursuant to Section 13 and 15(d)

Investment Income, Net (Schedule of Investment Income, Net) (Details)

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Investment Income, Net (Schedule of Investment Income, Net) (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
May 31, 2018
Feb. 28, 2018
Nov. 30, 2017
Aug. 31, 2017
May 31, 2017
Feb. 28, 2017
Nov. 30, 2016
Aug. 31, 2016
May 31, 2018
May 31, 2017
May 31, 2016
Investment Income, Net [Abstract]                      
Interest income on corporate funds                 $ 11.9 $ 9.9 $ 8.4
Interest expense                 (3.9) (2.5) (1.1)
Net gain/(loss) from equity-method investments                 0.6 (2.2) (2.8)
Investment income, net $ 2.5 $ 2.3 $ 1.7 $ 2.1 $ 1.6 $ 1.2 $ 0.9 $ 1.5 $ 8.6 $ 5.2 $ 4.5