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Stockholders' Equity - Schedule of Share Repurchases (Details) - USD ($)
$ / shares in Units, shares in Millions
 12 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Mar. 31, 2015
Oct. 31, 2016
Oct. 31, 2015
May 31, 2015
Stockholders' Equity Note [Abstract]            
Total Number of Shares Purchased 15.5 8.7 1.5      
Average price paid per share (in dollars per share) $ 141.16 $ 173.64 $ 226.55      
Approximate Dollar Value of Shares that May Yet Be Purchased Under the Programs            
Beginning balance $ 996,000,000 $ 0 $ 340,000,000      
Shares repurchased (2,250,000,000) (1,504,000,000) (340,000,000)      
Shares repurchase plans authorized       $ 4,000,000,000.0 $ 2,000,000,000 $ 500,000,000
Ending balance $ 2,746,000,000 $ 996,000,000 $ 0