Stock-Based Compensation (Tables)

The estimated assumptions used in the Black-Scholes valuation model to value our ESPP purchase rights were as follows:


	ESPP Purchase Rights
	Three Months Ended September 30,
	2020		2019
Risk-free interest rate	0.1	%	1.7 - 1.9%
Expected volatility	34 - 39%		34 - 37%
Weighted-average volatility	37	%	36	%
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,
	2020		2019		2020		2019
Cost of revenue	$	2	$	1	$	3	$	2
Research and development	74		61		140		110
Marketing and sales	12		10		23		17
General and administrative	25		20		49		36
Stock-based compensation expense	$	113	$	92	$	215	$	165

The following table summarizes our stock option activity for the six months ended September 30, 2020:


	Options (in thousands)	Weighted- Average Exercise Prices		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in millions)
Outstanding as of March 31, 2020	1,074	$	30.85
Granted	2	124.20
Exercised	(351)	28.27
Forfeited, cancelled or expired	—	—
Outstanding as of September 30, 2020	725	$	32.31	3.49	$	70
Vested and expected to vest	725	$	32.31	3.49	$	70
Exercisable as of September 30, 2020	725	$	32.31	3.49	$	70

The following table summarizes our restricted stock unit activity for the six months ended September 30, 2020:


	Restricted Stock Rights (in thousands)	Weighted- Average Grant Date Fair Values
Outstanding as of March 31, 2020	6,217	$	100.42
Granted	2,825	126.20
Vested	(1,645)	103.67
Forfeited or cancelled	(204)	106.79
Outstanding as of September 30, 2020	7,193	$	109.62

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, 2020:


	Performance- Based Restricted Stock Units (in thousands)	Weighted- Average Grant Date Fair Value
Outstanding as of March 31, 2020	579	$	110.51
Granted	—	—
Forfeited or cancelled	—	—
Outstanding as of September 30, 2020	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, 2020:


	Market-Based Restricted Stock Units (in thousands)	Weighted- Average Grant Date Fair Value
Outstanding as of March 31, 2020	1,898	$	128.41
Granted	874	145.78
Vested	(157)	113.72
Forfeited or cancelled	(398)	137.98
Outstanding as of September 30, 2020	2,217	$	134.58

The following table summarizes total shares repurchased during the three and six months ended September 30, 2020 and 2019:



(In millions)	Shares	Amount
Three months ended September 30, 2020	—	$	—
Six months ended September 30, 2020	0.7	$	78
Three months ended September 30, 2019	3.3	$	306
Six months ended September 30, 2019	6.5	$	611