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, except Per Share data, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total intrinsic value of stock options exercised	$ 4.6	$ 2.3	$ 5.0
Stock-based compensation cost (pretax)	9.3	6.3	12.2
Tax benefits related to stock-based compensation cost	$ 1.7	$ 0.8	$ 1.8
Weighted average grant date fair value per option	$ 10.37	$ 9.77	$ 9.30