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Senior Long-Term Debt And Other Debt (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Debt Instrument [Line Items] |  |  |
Senior long-term debt and other debt | $ 3,779,796 | $ 4,103,629 |
Senior long-term debt and other debt, estimated fair value | 3,400,000 | 3,500,000 |
Interest on senior long-term debt and other debt | 187,800 | 197,300 | $ 178,600
Revolving Credit Facility [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, capacity available | 300,000 |  |
Line of credit facility, increase (decrease), net | $ 200,000 |  |
Line of credit facility, unused capacity, commitment fee percentage | 0.20% |  |
Borrowings outstanding under the facility | $ 0 | 0 |
Revolving Credit Facility [Member] | Markel Ventures [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, capacity available | 680,000 |  |
Borrowings outstanding under the facility | 169,500 | 238,100 |
Revolving Credit Facility [Member] | Secured Letters Of Credit [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, capacity available | 200,000 |  |
Previous line of credit facility |  |  |
Debt Instrument [Line Items] |  |  |
Line of credit facility, capacity available | 300,000 |  |
Unsecured Senior Notes [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Senior long-term debt and other debt | 3,439,199 |  |
Other Debt [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Senior long-term debt and other debt | 340,597 | 416,738 |
Other Debt [Member] | Markel Ventures [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Senior long-term debt and other debt | $ 339,000 | 414,100 |
3.45% Unsecured Senior Notes due May 7 2052 | Unsecured Senior Notes [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument, interest rate | 3.45% |  |
Unsecured senior notes | $ 591,000 | 590,689 |
7.35% Unsecured Senior Notes Due August 15, 2034 [Member] | Unsecured Senior Notes [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument, interest rate | 7.35% |  |
Unsecured senior notes | $ 129,076 | 129,004 |
3.625% Unsecured Senior Notes Due March 30, 2023 [Member] | Unsecured Senior Notes [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Debt instrument, interest rate | 3.625% |  |
Unsecured senior notes | $ 0 | $ 249,940 |

X
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- Definition Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69B -Publisher FASB -URI https://asc.fasb.org//1943274/2147481568/470-20-55-69B Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 69C -Publisher FASB -URI https://asc.fasb.org//1943274/2147481568/470-20-55-69C Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1D -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481139/470-20-50-1D Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482907/825-10-50-10 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 470 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 + Details
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- Definition Amount of cash paid for interest, including, but not limited to, capitalized interest and payment to settle zero-coupon bond attributable to accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount; classified as operating and investing activities. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 230 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482913/230-10-50-2 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -SubTopic 10 -Topic 210 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)(a)(2)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 942 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1 + Details
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- Definition Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(16)(a)(2)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1 + Details
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