Investment Income, Net (Schedule of Investment Income, Net) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Nov. 30, 2018	Nov. 30, 2017		Nov. 30, 2018	Nov. 30, 2017
Investment Income, Net [Abstract]
Interest income on corporate funds	$ 2.8	$ 2.7		$ 6.0	$ 5.6
Interest expense	(0.8)	(1.3)		(1.7)	(2.1)
Net gain from equity-method investments	0.1	0.3		0.1	0.3
Investment income, net	$ 2.1	$ 1.7	[1]	$ 4.4	$ 3.8	[1]

[1] Amounts have been adjusted to reflect the adoption of Accounting Standards Codification ("ASC") Topic 606, "Revenue from Contracts with Customers" ("ASC Topic 606").