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INCOME TAXES
 12 Months Ended
Dec. 31, 2023
Income Tax Disclosure [Abstract]  
INCOME TAXES INCOME TAXES
The following table sets forth our provision for income taxes for the periods indicated:
 Years Ended December 31,
 202320222021
 
(Millions of dollars)
Current tax expense (benefit)
Federal$(3)$52 $3 
State12 12 9 
Total current tax expense9 64 12 
Deferred tax expense
Federal739 423 433 
State90 41 39 
Total deferred tax expense829 464 472 
Total provision for income taxes$838 $528 $484 
The following table is a reconciliation of our income tax provision for the periods indicated:
Years Ended December 31,
 202320222021
 
(Millions of dollars)
Income before income taxes$3,497 $2,250 $1,984 
Federal statutory income tax rate21.0 %21.0 %21.0 %
Provision for federal income taxes734 472 417 
State income taxes, net of federal benefit100 54 40 
Deferred tax rate change, inclusive of valuation allowance2 (1)6 
Excess tax benefits from share-based compensation1 (1)(2)
Other, net (a)1 4 23 
Income tax provision$838 $528 $484 
(a) The year ended December 31, 2021, includes $19 million impact from previously recognized gains on certain benefit plan investments.

The following table sets forth the tax effects of temporary differences that gave rise to significant portions of the deferred tax assets and liabilities as of the dates indicated:
December 31,
2023		December 31,
2022
Deferred tax assets
(Millions of dollars)
Employee benefits and other accrued liabilities$88 $82 
Federal net operating loss2,534 1,105 
State net operating loss and benefits492 196 
Derivative instruments— 19 
Interest expense limitation210 25 
Other20 5 
Total deferred tax assets3,344 1,432 
Valuation allowance for state net operating loss and tax credits
Carryforward expected to expire prior to utilization(240)(75)
Net deferred tax assets3,104 1,357 
Deferred tax liabilities
Excess of tax over book depreciation104 95 
Derivative instruments7 — 
Investment in partnerships (a)5,587 3,001 
Total deferred tax liabilities5,698 3,096 
Net deferred tax liabilities$2,594 $1,739 
(a) Due primarily to excess of tax over book depreciation.

In August 2022, the U.S. government enacted the IRA into law. The IRA includes a new corporate alternative minimum tax (CAMT) of 15% on the adjusted financial statement income (AFSI) of corporations with average AFSI exceeding $1.0 billion over a three-year period. The CAMT became effective for the 2023 tax year. We do not expect the CAMT to have an impact on our cash taxes in the 2024 tax year. However, when our CAMT liability is greater than our regular U.S. federal income tax liability for any particular year, the CAMT liability would effectively accelerate our future U.S. federal income tax obligations but provide an offsetting credit against our regular U.S. federal income tax liability for future years. As a result, we expect that any future impact will be limited to timing differences in future tax years.

As of December 31, 2023, we have federal net operating loss carryforwards of $12.1 billion, which have an indefinite carryforward period. We expect to generate taxable income and utilize these net operating loss carryforwards in future periods. We also have loss and credit carryovers in multiple states, $10.9 billion of which have an indefinite carryforward period and $1.2 billion of which will expire between 2024 and 2038. We have deferred tax assets related to federal and state net operating loss and credit carryforwards of $3.0 billion and $1.3 billion in 2023 and 2022, respectively. We believe that it is more likely than not that the tax benefits of certain state carryforwards will not be utilized; therefore, we recorded a valuation allowance, which was increased by $165 million and $6 million in 2023 and 2021, respectively, and reduced by $1 million in 2022 through net income.