Annual report pursuant to Section 13 and 15(d)

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

v3.7.0.1
Stock-Based Compensation Plans (Other Information Pertaining to Performance Shares) (Details) - Performance Shares [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 $ 54.97 [1] $ 42.48 $ 37.61
Total grant-date fair value of shares vested $ 7.8 $ 5.9 $ 3.5
[1] Performance shares granted assuming achievement of performance goals at target. Actual amount of shares to be earned may differ from this amount.