Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Share-based Payment Arrangement [Abstract]

The weighted average assumptions used in the model are as follows:


Expected volatility of stock price						91%
Risk-free interest rate						0.18%
Valuation period						3 years
Dividend yield						—%

Stock Based Compensation Activity

The activity related to RSUs consisted of (in thousands of shares):


			Number of Shares	Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in millions)
Time-based RSUs
	Outstanding at January 1, 2021		1,070	$	27.47
		Granted (a)	240	63.12
		Vested (b)	(575)	29.46
		Forfeited	(43)	31.37
	Outstanding and expected to vest at September 30, 2021 (c)		692	$	37.93	1.1	$	81
Performance-based and market-based RSUs
	Outstanding at January 1, 2021		988	$	32.41
		Granted (a)	236	62.27
		Vested (b)	—	—
		Forfeited	(324)	45.92
	Outstanding at September 30, 2021		900	$	35.37	1.5	$	105
	Outstanding and expected to vest at September 30, 2021 (c)		900	$	35.37	1.5	$	105

__________

(a)Reflects the maximum number of stock units assuming achievement of all performance-, market- and time-vesting criteria and does not include those for non-employee directors. The weighted-average fair value of time-based RSUs and performance-based and market-based RSUs granted during the nine months ended September 30, 2020 was $23.14 and $21.06, respectively.

(b)The total fair value of RSUs vested during the nine months ended September 30, 2021 and 2020 was $17 million and $19 million, respectively.

(c)Aggregate unrecognized compensation expense related to time-based RSUs and performance-based and market-based RSUs amounted to $36 million and will be recognized over a weighted average vesting period of 1.3 years.