Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2020

Stock-based compensation expense is as follows (in millions):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2020		2019		2020
Cost of sales	$	39	$	75	$	106	$	193
Fulfillment	301		316		895		993
Technology and content	966		1,267		2,719		3,649
Marketing	298		446		813		1,233
General and administrative	175		184		491		578
Total stock-based compensation expense	$	1,779	$	2,288	$	5,024	$	6,646

Restricted Stock Unit Activity

The following table summarizes our restricted stock unit activity for the nine months ended September 30, 2020 (in millions):


	Number of Units	Weighted-Average Grant-Date Fair Value
Outstanding as of December 31, 2019	14.3	$	1,458
Units granted	7.1	2,281
Units vested	(4.0)	1,168
Units forfeited	(1.0)	1,571
Outstanding as of September 30, 2020	16.4	1,879

Scheduled Vesting for Outstanding Restricted Stock Units

Scheduled vesting for outstanding restricted stock units as of September 30, 2020, is as follows (in millions):


	Three Months Ended December 31,	Year Ended December 31,
	2020	2021	2022	2023	2024	Thereafter	Total
Scheduled vesting—restricted stock units	1.8	5.7	5.4	2.4	0.9	0.2	16.4

Changes in Stockholders' Equity

The following table shows the changes in stockholders’ equity (in millions):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2020		2019		2020
Total beginning stockholders’ equity	$	53,061	$	73,728	$	43,549	$	62,060

Beginning and ending common stock	5		5		5		5

Beginning and ending treasury stock	(1,837)		(1,837)		(1,837)		(1,837)

Beginning additional paid-in capital	30,035		38,017		26,791		33,658
Stock-based compensation and issuance of employee benefit plan stock	1,782		2,290		5,026		6,649
Ending additional paid-in capital	31,817		40,307		31,817		40,307

Beginning accumulated other comprehensive income (loss)	(960)		(1,455)		(1,035)		(986)
Other comprehensive income (loss)	(469)		426		(394)		(43)
Ending accumulated other comprehensive income (loss)	(1,429)		(1,029)		(1,429)		(1,029)

Beginning retained earnings	25,818		38,998		19,625		31,220
Cumulative effect of changes in accounting principles (1)	—		—		7		—
Net income	2,134		6,331		8,320		14,109
Ending retained earnings	27,952		45,329		27,952		45,329

Total ending stockholders’ equity	$	56,508	$	82,775	$	56,508	$	82,775

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(1)We recorded cumulative effect adjustments related to the new lease standard in Q1 2019 and the new measurement of credit losses standard in Q1 2020.