Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation Plans (Narrative) (Details)

v3.5.0.2
Stock-Based Compensation Plans (Narrative) (Details) - USD ($)
shares in Millions, $ 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]      
Shares authorized for grant 44.1    
Shares available for future grants 22.2    
Stock-based compensation expense $ 34.6 $ 31.4 $ 26.3
Income tax benefits related to stock-based compensation 12.9 11.7 10.1
Total unrecognized compensation cost related to all unvested stock-based awards $ 60.8    
Weighted-average period in years of all unvested stock-based awards 2 years 10 months 24 days    
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock options granted 0.8    
Contractual life 10 years    
Total intrinsic value of stock options exercised $ 14.5 17.6 18.9
Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock options granted    
Total intrinsic value of stock options exercised $ 1.0    
Service period 2 years    
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Service period 1 year    
Director [Member] | Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 1 year    
Director [Member] | Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 1 year    
Management [Member] | Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 5 years    
Total Award [Member] | Officer [Member] | Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 63.00%    
Tranche One [Member] | Officer [Member] | Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 25.00%    
Tranche One [Member] | Officer [Member] | Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 23.50%    
Tranche One [Member] | Officer [Member] | Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 33.30%    
Tranche One [Member] | Management [Member] | Restricted Stock Units [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 20.00%    
Tranche Two [Member] | Officer [Member] | Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 39.50%    
Employee Stock Purchase Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense $ 0.0 $ 0.0 $ 0.0
Discount to the market price 5.00%    
Maximum [Member] | Tranche One [Member] | Officer [Member] | Performance Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting percentage 50.00%    
Maximum [Member] | Employee Stock Purchase Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Discount to the market price 15.00%