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Share-Based Compensation (Details) - USD ($)
shares in Millions, $ in Millions
3 Months Ended 6 Months Ended
Nov. 30, 2015
Nov. 30, 2014
Nov. 30, 2015
Nov. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Amount of shares issuable through two stock-based compensation plans 6.8   6.8  
Charges against income for share-based payment arrangements $ 1.2 $ 1.5 $ 2.9 $ 2.9
Unrecognized compensation expenses related to share-based payment arrangements $ 13.2   $ 13.2