Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2020

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, 2019 (1)		149,974		$	55.90						24,031		$	58.21
Granted		4,780		$	421.73						6,876		$	300.51
Exercised or released		(6,815	)	$	44.11						(9,620	)	$	72.26
Cancelled		(1,006	)	$	68.67						(2,498	)	$	82.31
Balance,    December 31, 2020		146,933		$	68.26	6.08		$	93.66		18,789		$	136.49
Vested and    expected to vest,    December 31, 2020		101,617		$	69.04		5.80	$	64.69		18,778		$	136.53
Exercisable and vested,    December 31, 2020		66,205		$	46.88		4.89	$	43.61

(1) Prior period results have been adjusted to give effect to the Stock Split. See Note 1, Overview, for details.

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. The weighted-average assumptions used in the Black-Scholes model for stock options are as follows:

	Year Ended December 31,
	2020			2019			2018
Risk-free interest rate		0.26	%		2.4	%		2.5	%
Expected term (in years)		3.9			4.5			4.7
Expected volatility		69	%		48	%		42	%
Dividend yield		0.0	%		0.0	%		0.0	%
Grant date fair value per share (1)	$	216.14		$	22.32		$	24.38

(1) Prior period results have been adjusted to give effect to the Stock Split. See Note 1, Overview, for details.

Summary of Operational Milestone Based on Revenue or Adjusted EBITDA

The achievement status of the operational milestones as of December 31, 2020 was as follows:

Total Annualized Revenue			Annualized Adjusted EBITDA
Milestone (in billions)		Achievement Status	Milestone (in billions)		Achievement Status
$	20.0	Achieved and certified	$	1.5	Achieved and certified
$	35.0	Probable	$	3.0	Achieved and certified
$	55.0	-	$	4.5	Achieved and certified
$	75.0	-	$	6.0	Probable
$	100.0	-	$	8.0	Probable
$	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,
	2020		2019		2018
Cost of revenues	$	281	$	128	$	109
Research and development		346		285		261
Selling, general and administrative		1,107		482		375
Restructuring and other		—		3		4
Total	$	1,734	$	898	$	749