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Stock-Based Compensation - Schedule of Stock Based Compensation Key Assumptions for Valuation (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
May 31, 2018
May 31, 2017
May 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]      
Weighted-average Black-Scholes value $ 55.72 $ 43.99 $ 52.40
Intrinsic value of options exercised $ 359 $ 274 $ 115
Expected lives 6 years 6 months 6 years 6 months 6 years 4 months 24 days
Expected volatility 23.00% 25.00% 28.00%
Risk-free interest rate 2.07% 1.64% 1.94%
Dividend yield 0.796% 0.719% 0.519%