Stock-Based Compensation (Tables)



	ESPP Purchase Rights
	Three Months Ended September 30,
	2019		2018
Risk-free interest rate	1.7 - 1.9%		2.2 - 2.5%
Expected volatility	34 - 37%		29	%
Weighted-average volatility	36	%	29	%
Expected term	6 - 12 months		6 - 12 months
Expected dividends	None		None

The following table summarizes stock-based compensation expense resulting from stock options, restricted stock units, market-based restricted stock units, performance-based restricted stock units, and the ESPP purchase rights included in our Condensed Consolidated Statements of Operations (in millions):



	Three Months Ended September 30,				Six Months Ended September 30,
	2019		2018		2019		2018
Cost of revenue	$	1	$	1	$	2	$	2
Research and development	61		39		110		86
Marketing and sales	10		9		17		16
General and administrative	20		17		36		32
Stock-based compensation expense	$	92	$	66	$	165	$	136

The following table summarizes our stock option activity for the six months ended September 30, 2019:



	Options (in thousands)		Weighted- Average Exercise Prices		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in millions)
Outstanding as of March 31, 2019	1,375		$	30.63
Granted	3		94.74
Exercised	(160	)	30.29
Forfeited, cancelled or expired	—		—
Outstanding as of September 30, 2019	1,218		$	30.81	4.36	$	79
Vested and expected to vest	1,218		$	30.81	4.36	$	79
Exercisable as of September 30, 2019	1,218		$	30.81	4.36	$	79

The following table summarizes our restricted stock unit activity for the six months ended September 30, 2019:



	Restricted Stock Rights (in thousands)		Weighted- Average Grant Date Fair Values
Outstanding as of March 31, 2019	4,960		$	111.03
Granted	3,699		92.57
Vested	(1,519	)	106.86
Forfeited or cancelled	(285	)	109.45
Outstanding as of September 30, 2019	6,855		$	102.06

The following table summarizes our performance-based restricted stock unit activity, presented with the maximum number of shares that could potentially vest, for the six months ended September 30, 2019:



	Performance- Based Restricted Stock Units (in thousands)	Weighted- Average Grant Date Fair Value
Outstanding as of March 31, 2019	579	$	110.51
Granted	—	—
Forfeited or cancelled	—	—
Outstanding as of September 30, 2019	579	$	110.51

The following table summarizes our market-based restricted stock unit activity, presented with the maximum number of shares that could potentially vest, for the six months ended September 30, 2019:



	Market-Based Restricted Stock Units (in thousands)		Weighted- Average Grant Date Fair Value
Outstanding as of March 31, 2019	958		$	155.64
Granted	785		105.05
Vested	(93	)	109.05
Forfeited or cancelled	(260	)	137.05
Outstanding as of September 30, 2019	1,390		$	133.66

The following table summarizes total shares repurchased during the three and six months ended September 30, 2019 and 2018:



	May 2017 Program			May 2018 Program			Total
(in millions)	Shares	Amount		Shares	Amount		Shares	Amount
Three months ended September 30, 2019	—	$	—	3.3	$	306	3.3	$	306
Six months ended September 30, 2019	—	$	—	6.5	611		6.5	$	611
Three months ended September 30, 2018	—	$	—	2.3	$	299	2.3	$	299
Six months ended September 30, 2018	0.6	$	76	4.0	523		4.6	$	599