Stock-Based Compensation (Tables)

Compensation expense for the stock plans, as reported in our consolidated statements of income, is as follows:


	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

Activity for PSUs classified as equity is as follows:


		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

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	%

Activity for RSUs classified as equity is as follows:


		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

Stock option activity is summarized as follows:


				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