Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Valuation Assumptions on PSU Grants

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 2020 are as follows:

	Year Ended December 31, 2020
Expected Volatility (based on our and our peer group historical daily stock prices)	23	%
Expected Life (equals the performance period)	3 years
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	0.85	%

Activity for CIUs

Activity for CIUs, which are classified as a liability, is as follows:

	Units
	(000s)
Outstanding at December 31, 2022	15,247
Granted	9,004
Vested1	(7,223)
Outstanding at December 31, 2023	17,028

1CIUs in the preceding table 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, 2023, the three-year performance period for the 2021 CIU grant was completed and the related awards vested, but the performance factor has not yet been applied. The performance factor will be applied during the first quarter of 2024, with payment of the awards at that time.

Schedule of Cash-based Payment Award, Cash-incentive Units, Valuation Assumptions

The fair value of CIUs is estimated at each reporting period using the Monte-Carlo simulation model. Key assumptions used to value CIUs granted are as follows:

	Assumptions as of the Year Ended December 31, 2023
	2023 Grant		2022 Grant
Expected Volatility (based on our and our peer group historical daily stock prices)	30	%	27	%
Expected Life (equals the performance period)	2 years		1 year
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	4.26	%	4.75	%

	Assumptions as of the Year Ended December 31, 2022
	2022 Grant		2021 Grant
Expected Volatility (based on our and our peer group historical daily stock prices)	30	%	33	%
Expected Life (equals the performance period)	2 years		1 year
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	4.26	%	4.60	%

	Assumptions as of the Year Ended December 31, 2021
	2021 Grant
Expected Volatility (based on our and our peer group historical daily stock prices)	50	%
Expected Life (equals the performance period)	2 years
Risk Free Interest Rate (based on U.S. Treasury yields at the date of grant)	0.71	%

Activity for Restricted Stock Units

Activity for RSUs, which are classified as equity, is as follows:

		Weighted Average
	Shares	Grant Date
	(000s)	Fair Value
Outstanding at December 31, 2022	2,182	$	27.20
Granted	780	45.56
Vested	(1,691)	29.54
Forfeited	(58)	31.86
Outstanding at December 31, 2023	1,213	35.51

Share-based Payment Arrangement, Cash-Settled Restricted Stock Units, Activity

Activity for cash-settled RSUs, which are classified as a liability, is as follows:

	Shares
	(000s)
Outstanding at December 31, 2022	23
Vested	(23)
Outstanding at December 31, 2023	—

Schedule of Compensation Cost for Share-based Payment Arrangements

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

	Year Ended December 31
	2023		2022		2021
	(in millions of dollars)
Performance Share Units	$	0.3	$	5.7	$	3.3
Cash Incentive Units	21.7		12.8		3.2
Restricted Stock Units and Cash-Settled Restricted Stock Units	40.6		32.7		25.5
Stock Success Units	0.9		0.9		2.8
Other	0.6		0.6		0.6
Total Compensation Expense, Before Income Tax	$	64.1	$	52.7	$	35.4
Total Compensation Expense, Net of Income Tax	$	57.5	$	47.3	$	31.1