Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 459	$ 194	$ 818	$ 286
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on available-for-sale marketable securities [net of tax provision of ($2), ($1), ($5) and ($1), respectively]	6	1	16	(3)
Reclassification adjustment for net (gains) losses on available-for-sale marketable securities included in investment and other income, net [net of tax provision of $0, $0, $0 and $0, respectively]	(1)	1	(1)	1
Other comprehensive income (loss)	5	2	15	(2)
Comprehensive income	$ 464	$ 196	$ 833	$ 284