Annual report pursuant to Section 13 and 15(d)

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

v3.7.0.1
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, 2017
May 31, 2016
May 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average grant-date fair value per share $ 60.83 $ 47.46 $ 41.70
Total grant-date fair value of shares vested $ 3.0 $ 3.0 $ 3.5