Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 668	$ 181	$ 1,697	$ 999
Other comprehensive income, net of tax
Net unrealized gains (losses) on available-for-sale marketable securities [net of tax benefit (provision) of $0, $1, ($6) and ($4), respectively]	2	(2)	26	14
Reclassification adjustment for net gains on available-for-sale marketable securities included in investment and other income, net [net of tax provision of $0, $1, $4 and $1, respectively]	(2)	(1)	(15)	(2)
Other comprehensive income (loss)	0	(3)	11	12
Comprehensive income	$ 668	$ 178	$ 1,708	$ 1,011