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Income Taxes (Reconciliations Of United States Corporate Income Tax Rate To Effective Tax Rate On Income Before Income Taxes) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Income Tax Disclosure [Abstract] |  |  |
U.S. corporate tax rate | 21.00% | 21.00% | 21.00%
State income taxes, net of U.S. federal income tax benefit, Percent | (1.00%) | 2.20% | (0.40%)
Tax-exempt investment income, percent | (0.60%) | 10.60% | (0.50%)
Foreign operations, percent | 0.40% | (3.50%) | 0.50%
Impairment of goodwill, percent | 0.00% | (11.10%) | 0.00%
Markel CATCo Re income not subject to tax, percent | (0.60%) | 12.50% | 0.00%
Other, percent | (0.40%) | 4.50% | 0.50%
Effective tax rate | 20.80% | 31.80% | 21.90%
Income taxes at U.S. corporate tax rate | $ 557,278 | $ (31,829) | $ 657,264
State income taxes, net of U.S. federal income tax benefit | 27,007 | 3,369 | 12,689
Tax-exempt investment income | (15,328) | (16,063) | (16,109)
Foreign operations | 10,854 | 5,335 | 14,443
Impairment of goodwill | 0 | 16,800 | 0
Markel CATCo Re income not subject to tax | (15,013) | (18,871) | 0
Other | (12,182) | (6,950) | 15,674
Income tax expense (benefit) | $ 552,616 | $ (48,209) | $ 683,961

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