Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2017

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



	Three Months Ended June 30,				Six Months Ended June 30,
	2016		2017		2016		2017
Cost of sales (1)	$	—	$	12	$	—	$	21
Fulfillment	186		261		302		425
Marketing	80		133		136		228
Technology and content	419		633		737		1,073
General and administrative	83		119		137		205
Total stock-based compensation expense	$	768	$	1,158	$	1,312	$	1,952

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(1)	Beginning in Q3 2016, stock-based compensation expense was recorded to cost of sales for eligible employees providing delivery services.

The following table summarizes our restricted stock unit activity for the six months ended June 30, 2017 (in millions):



	Number of Units		Weighted-Average Grant-Date Fair Value
Outstanding as of December 31, 2016	19.8		$	506
Units granted	6.1		906
Units vested	(3.5	)	382
Units forfeited	(0.9	)	592
Outstanding as of June 30, 2017	21.5		$	636

Scheduled vesting for outstanding restricted stock units as of June 30, 2017, is as follows (in millions):



	Six Months Ended December 31,	Year Ended December 31,
	2017	2018	2019	2020	2021	Thereafter	Total
Scheduled vesting—restricted stock units	3.4	7.4	6.9	2.7	0.8	0.3	21.5