Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 655	$ 459	$ 1,029	$ 818
Other comprehensive income, net of tax
Net unrealized gains on available-for-sale marketable securities [net of tax provision of $1, $2, $6 and $5, respectively]	1	6	24	16
Reclassification adjustment for net gains on available-for-sale marketable securities included in investment and other income, net [net of tax provision of $1, $0, $4 and $0, respectively]	(2)	(1)	(13)	(1)
Other comprehensive (loss) income	(1)	5	11	15
Comprehensive income	$ 654	$ 464	$ 1,040	$ 833