Stock-Based Compensation (Tables)

9 Months Ended

Dec. 31, 2015

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of assumptions used in the Black-Scholes valuation model

	Stock Option Grants		ESPP
	Nine Months Ended December 31,		Nine Months Ended December 31,
	2014		2015		2014
Risk-free interest rate	1.1 -1.9%		0.3 - 0.4%		0.04 - 0.1%
Expected volatility	36 - 40%		32	%	34 - 35%
Weighted-average volatility	38	%	32	%	35	%
Expected term	4.5 years		6 - 11.5 months		6 - 12 months
Expected dividends	None		None		None

Schedule Of Stock-Based Compensation Expense By Statement Of Operations

	Three Months Ended December 31,				Nine Months Ended December 31,
	2015		2014		2015		2014
Cost of revenue	$	—	$	1	$	1	$	2
Research and development	26		$	22	77		61
Marketing and sales	5		6		17		16
General and administrative	11		10		36		29
Stock-based compensation expense	$	42	$	39	$	131	$	108

Employee Stock Option [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Disclosure Of Stock-Based Compensation Arrangements By Stock-Based Payment Award

	Options (in thousands)		Weighted- Average Exercise Prices		Weighted- Average Remaining Contractual Term  (in years)	Aggregate Intrinsic Value (in millions)
Outstanding as of March 31, 2015	4,920		$	37.44
Granted	4		66.72
Exercised	(1,473	)	43.92
Forfeited, cancelled or expired	(52	)	35.76
Outstanding as of December 31, 2015	3,399		$	34.69	5.78	$	116
Vested and expected to vest	3,241		$	34.84	5.67	$	110
Exercisable as of December 31, 2015	2,263		$	36.18	4.57	$	74

Restricted Stock Rights [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Disclosure Of Stock-Based Compensation Arrangements By Stock-Based Payment Award

	Restricted Stock Rights (in thousands)		Weighted- Average Grant Date Fair Values
Balance as of March 31, 2015	10,855		$	26.20
Granted	2,743		64.45
Vested	(5,520	)	21.66
Forfeited or cancelled	(816	)	34.16
Balance as of December 31, 2015	7,262		$	43.20

Market-Based Restricted Stock Units [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Disclosure Of Stock-Based Compensation Arrangements By Stock-Based Payment Award

	Market-Based Restricted  Stock Units (in thousands)		Weighted- Average  Grant Date Fair Value
Balance as of March 31, 2015	663		$	31.82
Granted	395		79.81
Vested	(742	)	25.77
Vested above target	371		25.77
Forfeited or cancelled	(51	)	40.10
Balance as of December 31, 2015	636		$	64.49

Repurchase Program, Total [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Disclosure Of Stock-Based Compensation Arrangements By Stock-Based Payment Award

	May 2014 Program			May 2015 Program			Total
(in millions)	Shares	Amount		Shares	Amount		Shares	Amount
Three months ended December 31, 2015	—	$	—	1.8	$	126	1.8	$	126
Nine months ended December 31, 2015	1.0	$	57	4.8	$	327	5.8	$	384
Three months ended December 31, 2014	2.5	$	97	—	$	—	2.5	$	97
Nine months ended December 31, 2014	6.5	$	242	—	$	—	6.5	$	242