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, 2021	Mar. 31, 2020	Mar. 31, 2019
Available-for-sale debt securities:
Realized gains (losses)	$ 20	$ 9	$ (12)
Other-than-temporary impairment		(8)	0
Equity investments:
Unrealized gains recognized	114	41	14
Realized gains on sales	$ 15	$ 5	$ 0