The components of income before income taxes for each of the three years ended December 31, 2020 and income tax expense (benefit) attributable thereto were as follows:


	Years Ended December 31,
(Millions of dollars)	2020		2019		2018
Income (loss) before income taxes	$	509.1	$	202.4	$	273.9
Income tax expense (benefit)
Federal - Current	$	96.0	15.6		18.4
Federal - Deferred	4.7		21.7		31.0
State - Current and deferred	22.3		10.3		10.9
Total	$	123.0	$	47.6	$	60.3


	Years Ended December 31,
(Millions of dollars)	2020		2019		2018
Income tax expense based on the U.S. statutory tax rate	$	106.9	$	42.5	$	57.5
State income taxes, net of federal benefit	17.5		8.6		8.3

Federal credits	(1.9)		(2.3)		(2.0)
Other, net	0.5		(1.2)		(3.5)
Total	$	123.0	$	47.6	$	60.3

An analysis of the Company’s deferred tax assets and deferred tax liabilities at December 31, 2020 and 2019 showing the tax effects of significant temporary differences is as follows:


	December 31,
(Millions of dollars)	2020		2019
Deferred tax assets
Property costs and asset retirement obligations	$	4.5	$	3.7

Employee benefits	8.0		6.1
Operating leases liability	31.6		25.0
Other deferred tax assets	7.2		2.1
Total gross deferred tax assets	51.3		36.9


Deferred tax liabilities
Accumulated depreciation and amortization	(213.2)		(191.2)
State deferred taxes	(20.2)		(27.9)
Operating leases right of use assets	(31.0)		(24.8)
Other deferred tax liabilities	(5.3)		(9.7)
Total gross deferred tax liabilities	(269.7)		(253.6)
Net deferred tax liabilities	$	(218.4)	$	(216.7)

In management’s judgment, the net deferred tax assets in the preceding table will more likely than not be realized as reductions of future taxable income or by utilizing available tax planning strategies.

As of December 31, 2020, the earliest year remaining open for Federal and state audit and/or settlement is 2017 and 2015, respectively. Although the Company believes that recorded liabilities for unsettled issues are adequate, additional gains or losses could occur in future periods from resolution of outstanding unsettled matters.

The FASB’s rules for accounting for income tax uncertainties clarify the criteria for recognizing uncertain income tax benefits and require additional disclosures about uncertain tax positions. Under U.S. GAAP the financial statement recognition of the benefit for a tax position is dependent upon the benefit being more likely than not to be sustainable upon audit by the applicable taxing authority. If this threshold is met, the tax benefit is then measured and recognized at the largest amount that is greater than 50 percent likely of being realized upon ultimate settlement. Liabilities associated with uncertain income tax positions are included in Deferred Credits and Other Liabilities in the Consolidated Balance Sheets.

A reconciliation of the beginning and ending amount of the consolidated liability for unrecognized income tax benefits during the year ended December 31, 2020 and 2019 is shown in the following table.


	Year Ended December 31,
(Millions of dollars)	2020		2019
Balance at January 1	$	0.6	$	0.7
Additions for tax positions related to prior years	0.1		0.5

Settlements with taxing authorities	(0.3)		(0.6)


Balance at December 31	$	0.4	$	0.6

All additions or reductions to the above liability affect the Company’s effective tax rate in the respective period of change. The Company accounts for any applicable interest and penalties on uncertain tax positions as a component of income tax expense. Income tax expense for the years ended December 31, 2020, 2019 and 2018 included immaterial amounts of interest and penalties, associated with uncertain tax positions. Of these amounts shown in the table, $0.3 million and $0.5 million represent the amount of unrecognized tax benefits that, if recognized, would impact our effective tax rate.

During the next twelve months, the Company does not expect a material change to the liability for uncertain taxes. Although existing liabilities could be reduced by settlement with taxing authorities or lapse due to statute of limitations, the Company believes that the changes in its unrecognized tax benefits due to these events will not have a material impact on the Consolidated Income Statement during 2021.