Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Plans (Other Information Pertaining to Restricted Stock) (Details)

v3.5.0.2
Stock-Based Compensation Plans (Other Information Pertaining to Restricted Stock) (Details) - Restricted Stock [Member] - USD ($)
$ / shares in Units, $ 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]      
Weighted-average grant-date fair value of restricted awards granted $ 47.46 $ 41.70 $ 38.53
Total grant-date fair value of restricted stock vested $ 3.0 $ 3.5 $ 3.3