Stock-Based Compensation (Tables)

6 Months Ended

Sep. 30, 2017

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

Schedule of assumptions used in the Black-Scholes valuation model

	ESPP Purchase Rights
	Three Months Ended September 30,
	2017		2016
Risk-free interest rate	1.13 - 1.24%		0.5 - 0.6%
Expected volatility	28	%	29 - 32%
Weighted-average volatility	28	%	31	%
Expected term	6 - 12 months		6 - 12 months
Expected dividends	None		None

Schedule Of Stock-Based Compensation Expense By Statement Of Operations

	Three Months Ended September 30,				Six Months Ended September 30,
	2017		2016		2017		2016
Cost of revenue	$	1	$	1	$	2	$	2
Research and development	36		27		64		54
Marketing and sales	9		8		16		15
General and administrative	16		12		28		25
Stock-based compensation expense	$	62	$	48	$	110	$	96

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, 2017	2,377		$	33.35
Granted	2		105.99
Exercised	(744	)	40.47
Forfeited, cancelled or expired	(2	)	46.31
Outstanding as of September 30, 2017	1,633		$	30.19	5.91	$	143
Vested and expected to vest	1,633		$	30.19	5.91	$	143
Exercisable as of September 30, 2017	1,553		$	30.40	5.90	$	136

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
Outstanding as of March 31, 2017	5,153		$	65.03
Granted	1,881		110.72
Vested	(2,158	)	110.98
Forfeited or cancelled	(244	)	74.73
Outstanding as of September 30, 2017	4,632		$	61.67

Performance 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

	Performance- Based Restricted Stock Units (in thousands)	Weighted- Average Grant Date Fair Value
Outstanding as of March 31, 2017	—	$	—
Granted	796	110.51
Forfeited or cancelled	—	—
Outstanding as of September 30, 2017	796	$	110.51

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
Outstanding as of March 31, 2017	1,282		$	87.37
Granted	706		140.93
Vested	(430	)	76.27
Forfeited or cancelled	(216	)	91.88
Outstanding as of September 30, 2017	1,342		$	118.35

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 2015 Program			May 2017 Program			Total
(in millions)	Shares	Amount		Shares	Amount		Shares	Amount
Three months ended September 30, 2017	—	$	—	1.3	$	153	1.3	$	153
Six months ended September 30, 2017	0.3	$	31	2.4	$	272	2.7	$	303
Three months ended September 30, 2016	1.6	$	127	—	$	—	1.6	$	127
Six months ended September 30, 2016	3.5	$	256	—	$	—	3.5	$	256