Our stock compensation plans (collectively, the “Plans”) permit the grant of stock options, stock appreciation rights (“SARs”), performance share units, restricted stock, restricted stock units and other stock-based awards to employees and directors. Our current stock compensation plan, the 2017 Performance Plan, was adopted on April 10, 2017 and expires on April 9, 2027. A total of 18 million shares of our common stock may be issued in respect of grants made under the 2017 Performance Plan. Any shares of common stock that are subject to awards of stock options or SARs will be counted as one share for each share granted for purposes of the aggregate share limit and any shares of common stock that are subject to any other awards will be counted as 2 shares for each share granted for purposes of the aggregate share limit. In addition, shares of common stock that are subject to awards issued under the 2017 Performance Plan or certain prior stock compensation plans that expire according to their terms or are forfeited, terminated, canceled or surrendered or are settled, or can be paid, only in cash, or are surrendered in payment of taxes associated with such awards (other than stock options or SARs) will be available for issuance pursuant to a new award under the 2017 Performance Plan. Shares issued under our stock compensation plans are usually issued from shares of our common stock held in treasury.

Grants of stock options and SARs (collectively referred to as “options”) under the Plans generally have a graded vesting period of four years whereby one-fourth of the awards vest on each of the first four anniversaries of the grant date, an exercise price equal to the fair market value of one share of our common stock on the date of grant (i.e., the closing market price on that date) and a contractual term of ten years. The exercise of tandem SARs cancels an equivalent number of stock options and, conversely, the exercise of stock options cancels an equivalent number of tandem SARs. Option grants are cancelled on, or 90 days following, termination of employment unless termination is due to retirement, death or disability under certain circumstances, in which case, all outstanding options vest fully and remain outstanding for a term set forth in the related grant agreement.

	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (In millions)
Outstanding at January 1		4,998,021		$	20.61
Options granted		4,167,384			10.12
Options exercised		(20,218	)		12.68			$	—
Options expired		(370,938	)		12.44
Options cancelled		(73,517	)		18.83
Outstanding at December 31		8,700,732			15.97		5.9		3
Vested and expected to vest at December 31		8,604,644			16.00		5.9		3
Exercisable at December 31		4,462,091			20.98		2.9		—
Available for grant at December 31		6,659,546

In addition, the aggregate intrinsic value of options exercised in 2019 and 2018 was $3 million and $9 million, respectively.

Significant option groups outstanding at December 31, 2020 and related weighted average exercise price and remaining contractual term information follows:

Grant Date	Options Outstanding		Options Exercisable		Exercise Price			Remaining Contractual Term (Years)
2/25/2020		4,142,384		—	$	10.12			9.16
2/27/2017		556,409		465,203		35.26			6.16
2/22/2016		542,625		542,625		29.90			5.15
2/23/2015		493,730		493,730		27.16			4.15
2/24/2014		381,617		381,617		26.44			3.15
2/28/2013		904,580		904,580		12.98			2.16
2/27/2012		721,878		721,878		12.94			1.16
2/22/2011		523,979		523,979		13.91			0.15
All Other		433,530		428,479		⁽¹	⁾		⁽¹	⁾
		8,700,732		4,462,091

Weighted average grant date fair values of stock options and the assumptions used in estimating those fair values are as follows:

Performance share units granted under the Plans are earned over a three-year period beginning January 1 of the year of grant. Total units earned for grants made in 2020 may vary between 0% and 133%, and grants made during 2019 and 2018 may vary between 0% and 200% of the units granted based on the attainment of performance targets during the related three-year period and continued service. The performance targets are established by the Board of Directors. All of the units earned will be settled through the issuance of an equivalent number of shares of our common stock and are equity classified.

The following table summarizes the activity related to performance share units during 2020:

	Units			Weighted Average Grant Date Fair Value
Unvested at January 1		588,000		$	20.98
Units granted		171,871			7.59
Units vested		(154,141	)		29.04
Units forfeited		(10,950	)		20.92
Unvested at December 31		594,780			15.02

We measure the fair value of grants of performance share units based primarily on the closing market price of a share of our common stock on the date of the grant, modified as appropriate to take into account the features of such grants.

Restricted stock units granted under the Plans typically vest over a three-year period beginning on the date of grant. Restricted stock units will be settled through the issuance of an equivalent number of shares of our common stock and are equity classified.

The following table summarizes the activity related to restricted stock units during 2020:

	Units			Weighted Average Grant Date Fair Value
Unvested at January 1		2,734,475		$	23.21
Units granted		600,712			9.86
Units vested and settled		(646,444	)		24.50
Units forfeited		(119,870	)		18.80
Unvested at December 31		2,568,873			19.50

We measure the fair value of grants of restricted stock units based on the closing market price of a share of our common stock on the date of the grant.

Stock-based compensation expense, cash payments made to settle SARs and cash received from the exercise of stock options follows:


(In millions)	2020			2019			2018
Stock-based compensation expense recognized	$	31		$	27		$	16
Tax benefit		(8	)		(7	)		(4	)
After-tax stock-based compensation expense	$	23		$	20		$	12
Cash payments to settle SARs	$	—		$	—		$	1
Cash received from stock option exercises	$	—		$	2		$	9

As of December 31, 2020, unearned compensation cost related to the unvested portion of all stock-based awards was $22 million and is expected to be recognized over the remaining vesting period of the respective grants, through the fourth quarter of 2024.