Income Taxes (Tables)

12 Months Ended

Dec. 31, 2025

Income Tax Disclosure [Abstract]

Schedule of Components of Income Before Income Taxes And Income Tax Expense (Benefit)

The components of income (loss) before income taxes for each of the three years ended December 31, 2025 and income tax expense (benefit) attributable thereto are as follows:

	Years Ended December 31,
(Millions of dollars)	2025		2024		2023
Income (loss) before income taxes	$	609.2	$	651.6	$	734.4
Income tax expense (benefit)
Federal - Current	$	70.1	$	115.5	$	141.5
Federal - Deferred	48.4		11.8		3.5
State - Current and deferred	20.1		21.8		32.6
Total income tax expense (benefit)	$	138.6	$	149.1	$	177.6

Schedule of Reconciliation of Income Taxes Expense (Benefit) to Statutory Rate

The following table reconciles the Company income tax expense (benefit) based on the U.S. statutory tax rate to the income tax expense (benefit) for the year ended December 31, 2025, after the adoption of ASU 2023-09.

(Millions of dollars)	Amount		Percent
Income tax expense (benefit) based on the U.S. statutory tax rate	$	127.9	21.0	%
Domestic federal
Tax Credits	(8.0)		(1.3)	%
Nontaxable and nondeductible items	2.0		0.3	%
Other reconciling items	0.2		—	%
Domestic state and local income taxes, net of federal effect	16.5		2.8	%
Total income tax expense (benefit)	$	138.6	22.8	%

The following table reconciles income taxes based on the U.S. statutory tax rate to the Company’s income tax expense (benefit) for the years ended December 31, 2024 and 2023, prior to the adoption of ASU 2023-09.

	Years Ended December 31,
(Millions of dollars)	2024		2023
Income tax expense based on the U.S. statutory tax rate	$	136.8	$	154.2
State income taxes, net of federal benefit	17.3		25.0
Federal credits	(2.5)		(2.6)
Other, net	(2.5)		1.0
Total	$	149.1	$	177.6

Schedule of Cash Income Tax, Net of Refunds

Cash income taxes paid, net of refunds, for the year ended December, 31, 2025, was as follows:

(Millions of dollars)	Amount
US federal	$	86.0
US state and local	15.0
Total	$	101.0

Schedule of Deferred Tax Assets and Deferred Tax Liabilities

An analysis of the Company’s deferred tax assets and deferred tax liabilities at December 31, 2025 and 2024 showing the tax effects of significant temporary differences is as follows:

	December 31,
(Millions of dollars)	2025		2024
Deferred tax assets
Property costs and asset retirement obligations	$	8.1	$	7.3
Employee benefits	12.4		11.7
Operating leases liability	117.7		109.2
Other deferred tax assets	15.0		15.9
Total gross deferred tax assets	153.2		144.1
Deferred tax liabilities
Accumulated depreciation and amortization	(383.0)		(344.5)
State deferred taxes	(28.6)		(31.2)
Operating leases right-of-use assets	(110.5)		(103.5)
Other deferred tax liabilities	(19.6)		(8.3)
Total gross deferred tax liabilities	(541.7)		(487.5)
Net deferred tax liabilities	$	(388.5)	$	(343.4)

Schedule of Reconciliation of Beginning and Ending Liability for Uncertain Tax Positions

A reconciliation of the beginning and ending amount of the consolidated liability for unrecognized income tax benefits during the year ended December 31, 2025 and 2024 is shown in the following table:

	Years Ended December 31,
(Millions of dollars)	2025		2024
Balance at January 1	$	—	$	0.5
Additions for tax positions related to prior years	—		—
Expiration of statutes of limitation	—		(0.5)
Balance at December 31	$	—	$	—