Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option and RSU Activity

The following table summarizes our stock option and RSU activity:

	Stock Options								RSUs
						Weighted-						Weighted-
				Weighted-		Average	Aggregate					Average
	Number of			Average		Remaining	Intrinsic		Number			Grant
	Options			Exercise		Contractual	Value		of RSUs			Date Fair
	(in thousands)			Price		Life (years)	(in billions)		(in thousands)			Value
Balance, December 31, 2018		31,208		$	273.40					4,659		$	294.63
Granted		1,473		$	265.26					3,752		$	282.74
Exercised or released		(1,441	)	$	106.68					(1,949	)	$	277.13
Cancelled		(1,245	)	$	310.57					(1,656	)	$	295.05
Balance, December 31, 2019		29,995		$	279.49	6.89	$	4.17		4,806		$	291.06
Vested and expected to vest, December 31, 2019		15,860		$	228.29	6.05	$	3.02		4,804		$	291.05
Exercisable and vested, December 31, 2019		7,025		$	94.07	3.39	$	2.28

Schedule of Fair Value of Stock Option Award and ESPP on Grant Date

We use the fair value method in recognizing stock-based compensation expense. Under the fair value method, we estimate the fair value of each stock option award with service or service and performance conditions and the ESPP on the grant date generally using the Black-Scholes option pricing model and the weighted-average assumptions in the following table:

	Year Ended December 31,
	2019			2018			2017
Risk-free interest rate:
Stock options		2.4	%		2.5	%		1.8	%
ESPP		2.2	%		2.0	%		1.1	%
Expected term (in years):
Stock options		4.5			4.7			5.1
ESPP		0.5			0.5			0.5
Expected volatility:
Stock options		48	%		42	%		42	%
ESPP		53	%		43	%		35	%
Dividend yield:
Stock options		0.0	%		0.0	%		0.0	%
ESPP		0.0	%		0.0	%		0.0	%
Grant date fair value per share:
Stock options	$	111.59		$	121.92		$	122.25
ESPP	$	78.25		$	84.37		$	75.05

Summary of Operational Milestone Based on Revenue or Adjusted EBITDA

Total Annualized Revenue (in billions)		Annualized Adjusted EBITDA (in billions)
$20.0		$1.5
$35.0		$3.0
$55.0		$4.5
$75.0		$6.0
$100.0		$8.0
$125.0		$10.0
$150.0		$12.0
$ 175.0		$14.0

Summary of Stock-Based Compensation Expense

The following table summarizes our stock-based compensation expense by line item in the consolidated statements of operations (in millions):

	Year Ended December 31,
	2019		2018		2017
Cost of revenues	$	128	$	109	$	64
Research and development		285		261		218
Selling, general and administrative		482		375		185
Restructuring and other		3		4		—
Total	$	898	$	749	$	467