Stockholders' Equity - Share Repurchases (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Number of shares repurchased (in shares)	19,342,586	1,537,782	0
Average price per share (in dollars per share)	$ 69.20	$ 89.41	$ 0.00
Share repurchase amount	$ 1,339	$ 137	$ 0

Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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