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
Balance at Mar. 31, 2014	$ 2,422	$ 3	$ 2,353	$ 29	$ 37
Balance (in shares) at Mar. 31, 2014		311,442
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	840			875	(35)
Issuance of common stock	(24)		(24)
Issuance of common stock (in shares)		6,508
Reclassification of equity component of convertible notes	(31)		(31)
Repurchase and retirement of common stock	(337)		(337)			$ (337)
Stock repurchased and retired during period, Shares		(8,269)				8,200
Stock-based compensation	144		144
Tax benefit from stock-based compensation	22		22
Balance at Mar. 31, 2015	3,036	$ 3	2,127	904	2
Balance (in shares) at Mar. 31, 2015		309,681
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Total comprehensive income (loss)	1,138			1,156	(18)
Issuance of common stock	(49)		(49)
Issuance of common stock (in shares)		6,645
Reclassification of equity component of convertible notes	29		29
Settlement of convertible notes	(1)		(1)
Settlement of Convertible Notes		7,823
Exercise of convertible note hedge		(7,823)
Repurchase and retirement of common stock	(1,018)		(1,018)			$ (1,018)
Stock repurchased and retired during period, Shares		(15,724)				15,700
Stock-based compensation	178		178
Tax benefit from stock-based compensation	83		83
Balance at Mar. 31, 2016	$ 3,396	$ 3	1,349	2,060	(16)
Balance (in shares) at Mar. 31, 2016	301,000	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	(2,900)	(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	308,000	308,367