Under the Stock Incentive Plan of 2017 (the 2017 Plan), up to 17 million shares of common stock are available for awards to our employees, officers, consultants, and directors. Awards may be in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, performance share units, and other stock-based awards. Each full-value award, defined as any award other than a stock option or stock appreciation right, is counted as 1.76 shares. The exercise price for stock options issued cannot be less than the fair value of the underlying common stock as of the grant date. Stock options generally have a term of eight years after the date of grant and fully vest after three years. At December 31, 2019, approximately 13.9 million shares were available for future grants under the 2017 Plan.

Under the Stock Incentive Plan of 2012 (the 2012 Plan), which was terminated in May 2017 for the purposes of any further grants, up to 20 million shares of common stock were available for awards to our employees, officers, consultants, and directors. Awards could be in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, performance share units, and other stock-based awards. Each full-value award, defined as any award other than a stock option or stock appreciation right, is counted as 1.76 shares. Awards granted before the termination of the 2012 Plan remain outstanding in accordance with the plan's terms. Stock options generally have a term of eight years after the date of grant and fully vest after three years.

Under the Stock Incentive Plan of 2007 (the 2007 Plan), which was terminated in May 2012 for purposes of any further grants, up to 35 million shares of common stock were available for awards to our employees, officers, consultants, and directors. Awards could be in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, performance share units, and other stock-based awards. Each full-value award, defined as any award other than a stock option or stock appreciation right, is counted as 2.7 shares. Awards granted before the termination of the 2007 Plan remain outstanding in accordance with the plan's terms. Stock options generally have a term of eight years after the date of grant and fully vest after three years.


		Weighted Average
	Shares	Grant Date
	(000s)	Fair Value
Outstanding at December 31, 2018	283	$	51.33
Granted	205	41.57
Vested	(117)	55.31
Forfeited	(34)	50.40
Outstanding at December 31, 2019	337	44.11

During 2019, 2018, and 2017, we issued PSUs with a weighted average grant date fair value per share of $41.57, $44.19, and $51.37, respectively. Vesting for the PSUs occurs at the end of a three-year period and is contingent upon our achievement of prospective company performance goals and our total shareholder return relative to a board-approved peer group during the three-year period. Actual performance, including modification for relative total shareholder return, may result in the ultimate award of 40 to 180 percent of the initial number of PSUs issued, with the potential for no award if company performance goals are not achieved during the three-year period. Forfeitable dividend equivalents on PSUs are accrued in the form of additional PSUs.

PSU shares in the preceding table represent aggregate initial target awards and accrued dividend equivalents and do not reflect potential increases or decreases resulting from the application of the performance factor determined after the end of the performance periods. At December 31, 2019, the three-year performance period for the 2017 PSU grant was completed and the related shares vested, but the performance factor had not yet been applied. The performance factor will be applied during the first quarter of 2020, with distribution of the stock thereafter. Granted and vested amounts in the preceding table also include an adjustment to reflect the application of the performance factor to the 2016 PSU grant, which occurred during the first quarter of 2019.

At December 31, 2019, we had approximately $5.8 million of unrecognized compensation cost related to PSUs that will be recognized over a weighted average period of 1.6 years. The estimated compensation expense is adjusted for actual performance experience and is recognized ratably during the service period, or remaining service period, if and when it becomes probable that the performance conditions will be satisfied. Compensation cost for PSUs subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period.

The fair value of PSUs is estimated on the date of initial grant using the Monte-Carlo simulation model. Key assumptions used to value PSUs granted during the years shown are as follows:


	Year Ended December 31
	2019		2018		2017
Expected Volatility (based on our and our peer group historical daily stock prices)	23	%	24	%	24	%
Expected Life (equals the performance period)	3.0 years		3.0 years		3.0 years
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	2.53	%	2.32	%	1.52	%


		Weighted Average
	Shares	Grant Date
	(000s)	Fair Value
Outstanding at December 31, 2018	827	$	44.62
Granted	753	37.07
Vested	(487)	40.77
Forfeited	(49)	42.66
Outstanding at December 31, 2019	1,044	41.06

During 2019, 2018, and 2017, we issued RSUs with a weighted average grant date fair value per share of $37.07, $47.76, and $48.92, respectively. RSUs vest over a one to three-year service period, beginning at the date of grant, and the compensation cost is recognized ratably during the vesting period. Forfeitable dividend equivalents on RSUs are accrued in the form of additional RSUs. Compensation cost for RSUs subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period.

The total fair value of shares vested during 2019, 2018, and 2017 was $19.5 million, $18.1 million, and $13.3 million, respectively. At December 31, 2019, we had $20.0 million of unrecognized compensation cost related to RSUs that will be recognized over a weighted average period of 0.9 years.


				Remaining	Intrinsic
	Shares	Weighted Average		Contractual Term	Value
	(000s)	Exercise Price		(in years)	(in millions)
Outstanding at December 31, 2018	105	$	24.41

Exercised	(31)	25.18
Outstanding at December 31, 2019	74	24.09		0.7	$	0.4

Exercisable at December 31, 2019	74	$	24.09	0.7	$	0.4

All outstanding stock options at December 31, 2019 have vested. Stock options vest over a one to three-year service period, beginning at the date of grant, and the compensation cost is recognized ratably during the vesting period. Compensation cost for stock options subject to accelerated vesting at the date of retirement eligibility is recognized over the implicit service period. At December 31, 2019, we had no unrecognized compensation cost related to stock options.

The intrinsic value of options exercised in 2019, 2018, and 2017 was $0.3 million, $0.7 million, and $10.0 million, respectively. There were no stock options granted or vested in the years 2017 through 2019.


	Year Ended December 31
	2019		2018		2017
	(in millions of dollars)
Performance Share Units	$	5.0	$	6.8	$	11.5
Restricted Stock Units	21.0		19.0		17.5

Other	0.6		0.5		0.5
Total Compensation Expense, Before Income Tax	$	26.6	$	26.3	$	29.5

Total Compensation Expense, Net of Income Tax	$	22.7	$	20.9	$	19.5