Stock-Based Compensation (Tables)

9 Months Ended

Dec. 31, 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 December 31,
	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 December 31,				Nine Months Ended December 31,
	2017		2016		2017		2016
Cost of revenue	$	—	$	—	$	2	$	2
Research and development	38		27		102		81
Marketing and sales	8		8		24		23
General and administrative	17		13		45		38
Stock-based compensation expense	$	63	$	48	$	173	$	144

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	3		108.88
Exercised	(746	)	40.58
Forfeited, cancelled or expired	(2	)	45.15
Outstanding as of December 31, 2017	1,632		$	30.20	5.67	$	122
Vested and expected to vest	1,632		$	30.20	5.67	$	122
Exercisable as of December 31, 2017	1,612		$	30.24	5.66	$	121

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	3,661		109.33
Vested	(2,370	)	111.14
Forfeited or cancelled	(330	)	77.44
Outstanding as of December 31, 2017	6,114		$	73.01

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 December 31, 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 December 31, 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 December 31, 2017	—	$	—	1.4	$	150	1.4	$	150
Nine months ended December 31, 2017	0.3	$	31	3.8	$	422	4.1	$	453
Three months ended December 31, 2016	1.5	$	127	—	$	—	1.5	$	127
Nine months ended December 31, 2016	5.0	$	383	—	$	—	5.0	$	383