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Income Taxes - Components of Aon's Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Deferred tax assets: |  |
Net operating loss, capital loss, interest, and tax credit carryforwards | $ 1,576 | $ 1,049
Employee benefit plans | 359 | 337
Lease liabilities | 171 | 164
Other accrued expenses | 176 | 155
Federal and state benefit of interest from uncertain tax positions | 99 | 75
Accrued interest | 102 | 52
Deferred revenue | 31 | 25
Other | 56 | 40
Total | 2,570 | 1,897
Valuation allowance on deferred tax assets | (202) | (197)
Total | 2,368 | 1,700
Deferred tax liabilities: |  |
Intangibles and property, plant and equipment | (1,512) | (254)
Deferred costs | (160) | (149)
Lease right-of-use asset | (139) | (135)
Unremitted earnings | (66) | (44)
Other accrued expenses | (21) | (20)
Unrealized foreign exchange gains | (36) | (18)
Investment basis differences | 42 |
Investment basis differences |  | 49
Other | (57) | (49)
Total | (2,033) | (620)
Net deferred tax asset | $ 335 | $ 1,080

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- Definition The sum of the tax effects as of the balance sheet date of the amount of (1) excess of tax deductions over gross income in a year which cannot be used on the tax returns in the current year but can be carried forward to reduce taxable income or income taxes payable in a future year, for which there must be sufficient tax-basis income to utilize a portion or all of the carryforward amount to realize the deferred tax asset, and capital losses that cannot be utilized on the tax return during a period that have been carried forward to reduce taxable income or taxes payable in a future year and (2) future tax deductions arising from all unused tax credit carryforwards which have been reduced by a valuation allowance. + References No definition available. + Details
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