Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 181	$ 214	$ 999	$ 500
Other comprehensive income (loss), net of tax:
Net unrealized (losses) gains on available-for-sale marketable securities [net of tax benefit (provision) of $1, ($2), ($4) and ($3), respectively]	(2)	4	14	1
Reclassification adjustment for net (gains) losses on available-for-sale marketable securities included in investment and other income, net [net of tax provision (benefit) of $1, ($3), $1 and ($3), respectively]	(1)	8	(2)	9
Other comprehensive (loss) income	(3)	12	12	10
Comprehensive income	$ 178	$ 226	$ 1,011	$ 510