Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation Expense

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

	Year Ended December 31,
	2019		2020		2021
Cost of sales	$	149	$	283	$	540
Fulfillment	1,182		1,357		1,946
Technology and content	3,725		5,061		6,645
Marketing	1,135		1,710		2,530
General and administrative	673		797		1,096
Total stock-based compensation expense (1)	$	6,864	$	9,208	$	12,757

___________________

(1)The related tax benefits were $1.4 billion, $1.9 billion, and $2.7 billion for 2019, 2020, and 2021.

Summary of Restricted Stock Unit Activity

The following table summarizes our restricted stock unit activity (in millions):

	Number of Units	Weighted Average Grant-Date Fair Value
Outstanding as of January 1, 2019	15.9	$	1,024
Units granted	6.7	1,808
Units vested	(6.6)	827
Units forfeited	(1.7)	1,223
Outstanding as of December 31, 2019	14.3	1,458
Units granted	8.0	2,373
Units vested	(5.8)	1,239
Units forfeited	(1.3)	1,642
Outstanding as of December 31, 2020	15.2	2,004
Units granted	6.3	3,348
Units vested	(5.4)	1,704
Units forfeited	(2.1)	2,314
Outstanding as of December 31, 2021	14.0	2,684

Scheduled Vesting of Outstanding Restricted Stock Units

Scheduled vesting for outstanding restricted stock units as of December 31, 2021, is as follows (in millions):

	Year Ended
	2022	2023	2024	2025	2026	Thereafter	Total
Scheduled vesting — restricted stock units	5.4	5.2	2.2	0.9	0.1	0.2	14.0