Cash and Cash Equivalents and Investments in Marketable Securities - Schedule of Gains and Losses on Investments in Marketable Securities Presented in Our Consolidated Statement of Income (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Available-for-sale debt securities:
Realized gains (losses)	$ 9	$ (12)	$ 41
Other-than-temporary impairment	(8)	0	$ 0
Equity investments:
Unrealized gains recognized	41	14
Realized gains on sales	$ 5	$ 0