Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Other, tax expense (benefit)	$ (0.3)	$ 0.2	$ (0.2)
Less Than [Member]
Change in fair value of derivatives, tax expense	0.1	3.1	3.8
Change in fair value of available-for-sale securities, tax expense (benefit)	$ (0.1)	$ (0.1)	$ (0.1)