Stock Incentive Plans - Schedule of Stock-Based Compensation (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Share-based Payment Arrangement [Abstract]
Total share-based compensation cost	$ 68	$ 74	$ 93
Related income tax benefit	12	15	21
Total intrinsic value of options exercised	8	44	136
Tax benefits from exercised stock options and awards	$ 14	$ 39	$ 84

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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