Stockholders' Equity

3 Months Ended

Mar. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

STOCKHOLDERS’ EQUITY

Stock Repurchase Activity

In February 2016, the Board of Directors authorized a program to repurchase up to $5.0 billion of our common stock, with no fixed expiration. There were no repurchases of common stock in Q1 2017 or Q1 2018.

Stock Award Activity

Common shares outstanding plus shares underlying outstanding stock awards totaled 504 million as of December 31, 2017 and March 31, 2018. These totals include all vested and unvested stock awards outstanding, including those awards we estimate will be forfeited. Stock-based compensation expense is as follows (in millions):



	Three Months Ended March 31,
	2017		2018
Cost of sales	$	8	$	15
Fulfillment	163		244
Marketing	94		161
Technology and content	441		631
General and administrative	86		132
Total stock-based compensation expense	$	792	$	1,183

The following table summarizes our restricted stock unit activity for the three months ended March 31, 2018 (in millions):



	Number of Units		Weighted-Average Grant-Date Fair Value
Outstanding as of December 31, 2017	20.1		$	725
Units granted	0.7		1,464
Units vested	(1.1	)	440
Units forfeited	(0.6	)	750
Outstanding as of March 31, 2018	19.1		$	769

Scheduled vesting for outstanding restricted stock units as of March 31, 2018, is as follows (in millions):



	Nine Months Ended December 31,	Year Ended December 31,
	2018	2019	2020	2021	2022	Thereafter	Total
Scheduled vesting—restricted stock units	6.0	7.2	3.7	1.8	0.2	0.2	19.1

As of March 31, 2018, there was $6.0 billion of net unrecognized compensation cost related to unvested stock-based compensation arrangements. This compensation is recognized on an accelerated basis with approximately half of the compensation expected to be expensed in the next twelve months, and has a weighted-average recognition period of 1.1 years. The estimated forfeiture rate as of December 31, 2017 and March 31, 2018 was 28%. Changes in our estimates and assumptions relating to forfeitures may cause us to realize material changes in stock-based compensation expense in the future.