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Share-Based Compensation - Schedule of Stock Option Activity (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
 12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Shares    
Beginning balance (in shares) 4  
Granted (in shares) 1  
Cancelled (in shares) (1)  
Exercised (in shares) (1)  
Ending balance (in shares) 3 4
Weighted- Average Exercise Price    
Beginning balance (in dollars per share) $ 145.76  
Granted (in dollars per share) 157.45  
Cancelled (in dollars per share) 180.79  
Exercised (in dollars per share) 86.95  
Ending balance (in dollars per share) $ 161.27 $ 145.76
Weighted- Average Remaining Contractual Term (Years)    
Stock options outstanding, remaining contractual term 4 years 4 years
Stock options outstanding, aggregate intrinsic value $ 36 $ 97
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest [Abstract]    
Stock options vested and expected to vest (in shares) 3  
Stock options vested and exercisable (in shares) 2  
Stock options vested and expected to vest, weighted average exercise price (in dollars per share) $ 160.28  
Stock options vested and exercisable, weighted average exercise price (in dollars per share) $ 147.76  
Stock options vested and expected to vest, weighted average remaining contractual term 4 years  
Stock options vested and exercisable, weighted average remaining contractual term 2 years  
Stock options vested and expected to vest, aggregate intrinsic value $ 35  
Stock options vested and exercisable, aggregate intrinsic value $ 35