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Income Taxes - Components of Aon's deferred tax assets and liabilities (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Deferred tax assets: |  |
Net operating loss, capital loss, interest, and tax credit carryforwards | $ 653 | $ 440
Employee benefit plans | 312 | 373
Lease liabilities | 248 | 247
Other accrued expenses | 103 | 68
Deferred revenue | 36 | 24
Investment basis differences | 28 | 28
Lease and service guarantees | 2 | 3
Accrued interest | 0 | 116
Other | 54 | 57
Total | 1,436 | 1,356
Valuation allowance on deferred tax assets | (205) | (200)
Total | 1,231 | 1,156
Deferred tax liabilities: |  |
Intangibles and property, plant and equipment | (291) | (251)
Lease right-of-use asset | (211) | (219)
Deferred costs | (141) | (128)
Unremitted earnings | (37) | (28)
Unrealized foreign exchange gains | (26) | (26)
Other accrued expenses | (22) | (25)
Other | (41) | (33)
Total | (769) | (710)
Net deferred tax asset | $ 462 | $ 446

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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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