Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 795	$ 3,410	$ 267
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on available-for-sale marketable securities [net of tax (provision) benefit of ($5), $6 and $0, respectively]	11	(29)	(1)
Reclassification adjustment for net losses (gains) on available-for-sale marketable securities included in investment and other income, net [net of tax (benefit) provision of ($3), $16 and $87, respectively]	9	(25)	(139)
Other comprehensive income (loss)	20	(54)	(140)
Comprehensive income	$ 815	$ 3,356	$ 127