Summary of Significant Accounting Policies (Foreign Currency Translation) (Details) - USD ($) $ in Millions	12 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Net gain (loss) on foreign currency forward contracts	$ (4)	$ 50	$ (16)
Net gain (loss) on foreign currency transactions	$ 11	$ (9)	$ 18

Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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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
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