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Share-Based Awards and Options - Valuation Assumptions (Details)
6 Months Ended
Nov. 30, 2015
Nov. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 1.62% 1.57%
Expected volatility 28.65% 23.65%
Dividend yield 0.10% 0.13%
Employee stock option    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (years) 5 years 5 years