Stockholders' Equity (Tables)

3 Months Ended

Mar. 31, 2019

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



	Three Months Ended March 31,
	2018		2019
Cost of sales	$	15	$	24
Fulfillment	244		234
Marketing	161		209
Technology and content	631		675
General and administrative	132		132
Total stock-based compensation expense	$	1,183	$	1,274

The following table summarizes our restricted stock unit activity for the three months ended March 31, 2019 (in millions):



	Number of Units		Weighted-Average Grant-Date Fair Value
Outstanding as of December 31, 2018	15.9		$	1,024
Units granted	0.6		1,677
Units vested	(1.2	)	627
Units forfeited	(0.4	)	1,023
Outstanding as of March 31, 2019	14.9		$	1,080

Scheduled vesting for outstanding restricted stock units as of March 31, 2019, is as follows (in millions):



	Nine Months Ended December 31,	Year Ended December 31,
	2019	2020	2021	2022	2023	Thereafter	Total
Scheduled vesting—restricted stock units	5.6	5.5	2.5	1.0	0.2	0.1	14.9

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



	Three Months Ended March 31,
	2018			2019
Total beginning stockholders' equity	$	27,709		$	43,549

Beginning and ending common stock	5			5

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

Beginning additional paid-in capital	21,389			26,791
Stock-based compensation and issuance of employee benefit plan stock	1,174			1,268
Ending additional paid-in capital	22,563			28,059

Beginning accumulated other comprehensive loss	(484		)	(1,035		)
Other comprehensive income (loss)	17			25
Ending accumulated other comprehensive loss	(467		)	(1,010		)

Beginning retained earnings	8,636			19,625
Cumulative effect of changes in accounting principles (1)	934			7
Net income	1,629			3,561
Ending retained earnings	11,199			23,193

Total ending stockholders’ equity	$	31,463		$	48,410

___________________


(1)	We recorded cumulative effect adjustments related to the new revenue and income tax standards in Q1 2018 and the new lease standard in Q1 2019. See Item 1 of Part I, “Financial Statements — Note 1 — Accounting Policies — Accounting Pronouncements Recently Adopted” for additional information.