Our income tax expense consisted of the following for the year ended December 31 (in millions):

The U.S. federal statutory income tax rate is reconciled to the effective income tax rate for the year ended December 31 as follows:

The comparability of our income tax expense for the reported periods has been primarily affected by (i) variations in our income before income taxes; (ii) federal tax credits; (iii) the tax implications of impairments; (iv) excess tax benefits associated with equity-based compensation transactions; (v) the realization of state net operating losses and credits; (vi) tax audit settlements; (vii) adjustments to our accruals and deferred taxes and (viii) the impacts of enactment of tax reform.

For financial reporting purposes, income before income taxes by source for the year ended December 31 was as follows (in millions):

(a)	Foreign income before income taxes for the year ended December 31, 2019 includes a $52 million impairment charge related to our minority-owned investment in a waste conversion technology business. See Note 12 for further discussion.

Investments Qualifying for Federal Tax Credits — We have significant financial interests in entities established to invest in and manage low-income housing properties. We support the operations of these entities in exchange for a pro-rata share of the tax credits they generate. The low-income housing investments qualify for federal tax credits that we expect to realize through 2030 under Section 42 or Section 45D of the Internal Revenue Code. We also held a residual financial interest in an entity that owns a refined coal facility that qualified for federal tax credits under Section 45 of the Internal Revenue Code through 2019. The entity sold the majority of its assets in the first quarter of 2020, which resulted in a $7 million non-cash impairment of our investment at that time. We account for our investments in these entities using the equity method of accounting, recognizing our share of each entity’s results of operations and other reductions in the value of our investments in equity in net losses of unconsolidated entities within our Consolidated Statements of Operations.

During the years ended December 31, 2020, 2019 and 2018, we recognized $73 million (including the $7 million impairment of the refined coal facility noted above), $46 million and $30 million of net losses, respectively, and a reduction in our income tax expense of $87 million, $96 million and $57 million, respectively, primarily due to tax credits realized from these investments. In addition, during the years ended December 31, 2020, 2019 and 2018, we recognized interest expense of $11 million, $9 million and $3 million, respectively, associated with our investments in low-income housing properties. See Note 19 for additional information related to these unconsolidated variable interest entities.

Other Federal Tax Credits — During 2020, 2019 and 2018, we recognized federal tax credits in addition to the tax credits realized from our investments in low-income housing properties and the refined coal facility, resulting in a reduction in our income tax expense of $7 million, $11 million and $10 million, respectively.

Non-Deductible Transaction Costs — During 2020 and 2019, we recognized the detrimental tax impact of $27 million and $10 million, respectively, of non-deductible transaction costs related to our acquisition of Advanced Disposal. The tax rules require the capitalization of certain facilitative costs on the acquisition of stock of a company resulting in the applicable costs not being deductible for tax purposes.

Tax Implications of Impairments — Portions of the impairment charges recognized during 2019 and 2018 were not deductible for tax purposes resulting in an increase in income tax expense of $15 million and $1 million, respectively. The non-cash impairment charges recognized during 2020 were deductible for tax purposes. See Note 12 for more information related to our impairment charges.

Equity-Based Compensation — During 2020, 2019 and 2018, we recognized excess tax benefits related to the vesting or exercise of equity-based compensation awards resulting in a reduction in our income tax expense of $27 million, $25 million and $17 million, respectively.

State Net Operating Losses and Credits — During 2020, 2019 and 2018, we recognized state net operating losses and credits resulting in a reduction in our income tax expense of $12 million, $14 million and $22 million, respectively.

Tax Audit Settlements — We file income tax returns in the U.S. and Canada, as well as other state and local jurisdictions. We are currently under audit by various taxing authorities, as discussed below, and our audits are in various stages of completion. During the reported periods, we settled various tax audits which resulted in a reduction in our income tax expense of $10 million, $2 million and $40 million for the years ended December 31, 2020, 2019 and 2018, respectively.

We participate in the IRS’s Compliance Assurance Process, which means we work with the IRS throughout the year towards resolving any material issues prior to the filing of our annual tax return. Any unresolved issues as of the tax return filing date are subject to routine examination procedures. We are currently in the examination phase of IRS audits for the 2017 through 2020 tax years and expect these audits to be completed within the next 15 months. We are also currently undergoing audits by various state and local jurisdictions for tax years that date back to 2014.

Adjustments to Accruals and Deferred Taxes — Adjustments to our accruals and deferred taxes due to the filing of our income tax returns, analysis of our deferred tax balances and changes in state and foreign laws resulted in a reduction in our income tax expense of $3 million, $22 million and $52 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Enactment of Tax Reform – In accordance with applicable accounting guidance, the Company recognized the provisional tax impacts and subsequent measurement period adjustments related to the remeasurement of our deferred income tax assets and liabilities and the one-time, mandatory transition tax on deemed repatriation of previously tax-deferred and unremitted foreign earnings, resulting in a reduction in our income tax expense of $12 million for the year ended December 31, 2018.

Unremitted Earnings in Foreign Subsidiaries — In the third quarter of 2020, we modified our permanent reinvestment assertion and began providing additional income taxes for the undistributed current year earnings of our foreign subsidiaries. No additional income taxes have been provided for any remaining undistributed foreign earnings prior to 2020 not subject to the one-time, mandatory transition tax, or any additional outside basis difference, as these amounts continue to be indefinitely reinvested in foreign operations.

Deferred Tax Assets (Liabilities)

The components of net deferred tax liabilities as of December 31 are as follows (in millions):


	2020		2019
Deferred tax assets:
Net operating loss, capital loss and tax credit carry-forwards	$	186	$	150
Landfill and environmental remediation liabilities		57		156
Operating lease liabilities		131		114
Miscellaneous and other reserves, net		99		150
Subtotal		473		570
Valuation allowance		(150)		(162)
Deferred tax liabilities:
Property and equipment		(956)		(842)
Goodwill and other intangibles		(1,059)		(865)
Operating lease right-of-use assets		(114)		(108)
Net deferred tax liabilities	$	(1,806)	$	(1,407)

As of December 31, 2020, we had $15 million of federal net operating loss carry-forwards with expiration dates through 2025 and $2.3 billion of state net operating loss carry-forwards with expiration dates through 2040. We also had $37 million of foreign tax credit carry-forwards with expiration dates through 2030 and $16 million of state tax credit carry-forwards with expiration dates through 2036.

We have established valuation allowances for uncertainties in realizing the benefit of certain tax loss and credit carry-forwards and other deferred tax assets. While we expect to realize the deferred tax assets, net of the valuation allowances, changes in estimates of future taxable income or in tax laws may alter this expectation.

Liabilities for Uncertain Tax Positions

A reconciliation of the beginning and ending amount of gross unrecognized tax benefits, including accrued interest, is as follows (in millions):


	2020		2019		2018
Balance as of January 1	$	40	$	36	$	109
Additions based on tax positions related to the current year		5		5		6
Additions based on tax positions of prior years		—		—		12
Accrued interest		2		2		2
Settlements		—		—		(88)
Lapse of statute of limitations		(10)		(3)		(5)
Balance as of December 31	$	37	$	40	$	36

These liabilities are included as a component of other long-term liabilities in our Consolidated Balance Sheets because the Company does not anticipate that settlement of the liabilities will require payment of cash within the next 12 months. As of December 31, 2020, we had $31 million of net unrecognized tax benefits that, if recognized in future periods, would impact our effective income tax rate.

We recognize interest expense related to unrecognized tax benefits in our income tax expense, which was not material for the reported periods. We did not have any accrued liabilities or expense for penalties related to unrecognized tax benefits for the reported periods.