Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 359	$ 92
Other comprehensive income (loss), net of tax:
Net unrealized gains (losses) on available-for-sale marketable securities [net of tax provision of ($3) and $0, respectively]	10	(4)
Other comprehensive income (loss)	10	(4)
Comprehensive income	$ 369	$ 88