Derivative Instruments and Hedging Activities - Schedule of Interest Rate Swap (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Nov. 30, 2014	Nov. 30, 2013	Nov. 30, 2014	Nov. 30, 2013
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Amount of gain (loss) recognized in OCI	$ (0.6)	$ 4.5	$ 4.7	$ 26.2
Amount of (gain) loss reclassified from accumulated OCI into interest expense (effective portion)	2.5	6.8	7.3	14.3
Amount (gain) loss recognized in other income (expense) (ineffective portion and amount excluded from effectiveness testing)	$ 0	$ 21.8		$ 21.8