Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 913	$ 795	$ 3,410
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on available-for-sale marketable securities [net of tax (provision) benefit of ($4), ($5) and $6, respectively]	13	11	(29)
Reclassification adjustment for net (gains) losses on available-for-sale marketable securities included in investment and other income, net [net of tax (benefit) provision of $0, ($3) and $16, respectively]	(1)	9	(25)
Other comprehensive income (loss)	12	20	(54)
Comprehensive income	$ 925	$ 815	$ 3,356