Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Weighted Average Assumptions Used

During the years ended December 31, 2021 and 2019, we did not issue any stock unit awards containing a market condition.

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

Annual Activity of RSUs

Annual activity related to stock units 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)	245	65.23
		Vested (b)	(590)	29.16
		Forfeited	(54)	31.82
	Outstanding and expected to vest at December 31, 2021 (c)		671	$	39.39	0.9	$	139
Performance-based and market-based RSUs
	Outstanding at January 1, 2021		988	$	32.41
		Granted (a)	236	62.27
		Vested (b)	—	—
		Forfeited	(338)	45.39
	Outstanding at December 31, 2021		886	$	35.40	1.3	$	184
	Outstanding and expected to vest at December 31, 2021 (c)		886	$	35.40	1.3	$	184

__________

(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, which are discussed separately below. The weighted-average fair value of time-based RSUs, and performance-based and market-based RSUs granted in 2020 was $23.14 and $21.06, respectively, and the weighted-average fair value of time-based RSUs and performance-based RSUs granted in 2019 was $34.14 and $34.56, respectively.

(b)The total fair value of RSUs vested during 2021, 2020 and 2019 was $17 million, $19 million and $18 million, respectively.

(c)Aggregate unrecognized compensation expense related to time-based RSUs and performance-based and market-based RSUs amounted to $31 million and will be recognized over a weighted average vesting period of 1.1 years.