Stockholders' Equity - Share Repurchases (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)	15,933,651	19,342,586
Average price per share (in dollars per share)	$ 46.21	$ 69.20
Share repurchase amount	$ 736	$ 1,339
Open market purchases
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)	12,279,107	19,342,586
Average price per share (in dollars per share)	$ 43.67	$ 69.20
Share repurchase amount	$ 536	$ 1,339
ASR
Equity, Class of Treasury Stock [Line Items]
Number of shares repurchased (in shares)	3,654,544
Average price per share (in dollars per share)	$ 54.73
Share repurchase amount	$ 200

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