Capital Stock and Stock-Based Awards (Details) - Schedule of Intrinsic value of stock options exercised, pretax stock-based compensation cost and related tax benefits (USD $) In Millions, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Schedule of Intrinsic value of stock options exercised, pretax stock-based compensation cost and related tax benefits [Abstract]
Total intrinsic value of stock options exercised	$ 2.3	$ 5.0	$ 0.4
Stock-based compensation cost (pretax)	6.3	12.2	13.7
Tax benefits related to stock-based compensation cost	0.8	1.8	1.8
Weighted average grant date fair value per option	$ 9.77	$ 9.30	$ 8.15