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Stock Based Compensation (Details 3) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
May 31, 2016
May 31, 2015
May 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]      
Stock-based compensation valuation method Black-Scholes    
Weighted-average Black-Scholes value $ 52.40 $ 53.33 $ 35.79
Intrinsic value of options exercised $ 115 $ 253 $ 347
Expected lives 6.4 years 6.3 years 6.2 years
Expected volatility 28.00% 34.00% 35.00%
Risk-free interest rate 1.94% 2.02% 1.47%
Dividend Yield 0.519% 0.448% 0.561%