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SHARE-BASED AWARDS AND OPTIONS - Valuation Assumptions (Details) - Employee stock option
9 Months Ended
Feb. 29, 2016
Feb. 28, 2015
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%
Expected life (years) 5 years 5 years