Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Plans (Restricted Stock Activity) (Details)

v3.5.0.2
Stock-Based Compensation Plans (Restricted Stock Activity) (Details) - Restricted Stock [Member] - $ / shares
shares in Millions
12 Months Ended
May 31, 2016
May 31, 2015
May 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested, Beginning balance, Awards 0.2    
Granted, Awards    
Vested, Awards (0.1)    
Forfeited, Awards    
Nonvested, Ending balance, Awards 0.1 0.2  
Nonvested, Beginning balance, Weighted-average grant-date fair value per share $ 38.99    
Granted, Weighted-average grant-date fair value per share 47.46 $ 41.70 $ 38.53
Vested, Weighted-average grant-date fair value per share 37.70    
Forfeited, Weighted-average grant-date fair value per share 40.54    
Nonvested, Ending balance, Weighted-average grant-date fair value per share $ 43.99 $ 38.99