Stock-Based Compensation (Tables)

The assumptions used in the Monte-Carlo simulation model to value our market-based restricted stock units were as follows:



	Three Months Ended June 30,
	2019		2018
Risk-free interest rate	1.8	%	2.6	%
Expected volatility	15 - 61%		16 - 47%
Weighted-average volatility	29	%	28	%
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 June 30,
	2019		2018
Cost of revenue	$	1	$	1
Research and development	49		47
Marketing and sales	7		7
General and administrative	16		15
Stock-based compensation expense	$	73	$	70

The following table summarizes our stock option activity for the three months ended June 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	1		94.86
Exercised	(95	)	28.04
Forfeited, cancelled or expired	—		—
Outstanding as of June 30, 2019	1,281		$	30.89	4.59	$	90
Vested and expected to vest	1,281		$	30.89	4.59	$	90
Exercisable as of June 30, 2019	1,281		$	30.89	4.59	$	90

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



	Restricted Stock Rights (in thousands)		Weighted- Average Grant Date Fair Values
Outstanding as of March 31, 2019	4,960		$	111.03
Granted	3,486		92.56
Vested	(1,314	)	107.08
Forfeited or cancelled	(124	)	114.03
Outstanding as of June 30, 2019	7,008		$	102.53

The following table summarizes our performance-based restricted stock unit activity, presented with the maximum number of shares that could potentially vest, for the three months ended June 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 June 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 three months ended June 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 June 30, 2019	1,390		$	133.66

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



	May 2017 Program			May 2018 Program			Total
(in millions)	Shares	Amount		Shares	Amount		Shares	Amount
Three months ended June 30, 2019	—	$	—	3.2	$	305	3.2	$	305
Three months ended June 30, 2018	0.6	$	76	1.7	$	224	2.3	$	300