Consolidated Statements Of Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Additional paid-in capital	Retained earnings (Accumulated deficit)	Accumulated other comprehensive income (loss)	Repurchase program, total	Difference between Revenue Guidance in Effect before and after Topic 606 [Member]	Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Retained earnings (Accumulated deficit)	Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Accumulated other comprehensive income (loss)	ASU 2018-02 [Member]	ASU 2018-02 [Member] Retained earnings (Accumulated deficit)	ASU 2018-02 [Member] Accumulated other comprehensive income (loss)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	$ 34
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(37)
Balance at Mar. 31, 2016	3,396	$ 3	$ 1,349	$ 2,060	$ (16)
Balance (in shares) at Mar. 31, 2016		300,602
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	964			967	(3)
Issuance of common stock	(55)		(55)
Issuance of common stock (in shares)		4,626
Reclassification of equity component of convertible notes	2		2
Settlement of convertible notes	0		0
Settlement of Convertible Notes		(2,917)
Exercise of convertible note hedge		2,917
Repurchase and retirement of common stock	(508)		(508)			$ (508)
Stock repurchased and retired during period, Shares		(6,506)				6,500
Settlement of warrants		9,645
Stock-based compensation	196		196
Tax benefit from stock-based compensation	65		65
Balance at Mar. 31, 2017	4,060	$ 3	1,049	3,027	(19)
Balance (in shares) at Mar. 31, 2017		308,367
Cumulative Effect on Retained Earnings, before Tax			9
Cumulative Effect on Retained Earnings, Net of Tax				(8)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(107)
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(1)
Cumulative Effect on Retained Earnings, Tax	1						$ 612
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	935			1,043	(108)
Issuance of common stock	(42)		(42)
Issuance of common stock (in shares)		3,332
Repurchase and retirement of common stock	(601)		(601)			$ (601)
Stock repurchased and retired during period, Shares		(5,329)				5,300
Stock-based compensation	242		242
Balance at Mar. 31, 2018	$ 4,595	$ 3	657	4,062	(127)
Balance (in shares) at Mar. 31, 2018	306,000	306,370
Cumulative Effect on Retained Earnings, Net of Tax								$ 590			$ (1)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	$ 81								$ 22
Reclassification from Accumulated Other Comprehensive Income (Loss), Current Period, Net of Tax	(7)											$ 1
Cumulative Effect on Retained Earnings, Tax										$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	1,093			1,019	74
Issuance of common stock	(61)		(61)
Issuance of common stock (in shares)		2,722
Repurchase and retirement of common stock	1,192		880	312		$ (1,192)
Stock repurchased and retired during period, Shares		(10,985)				11,000
Stock-based compensation	284		284
Balance at Mar. 31, 2019	$ 5,331	$ 3	$ 0	$ 5,358	$ (30)
Balance (in shares) at Mar. 31, 2019	298,000	298,107