Summary Of Significant Accounting Policies	6 Months Ended
Jun. 30, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies a) Basis of Presentation. Markel Corporation is a diverse financial holding company serving a variety of niche markets. Markel Corporation's principal business markets and underwrites specialty insurance products and programs. Through its wholly-owned subsidiary, Markel Ventures, Inc. (Markel Ventures), Markel Corporation also owns interests in various industrial and service businesses that operate outside of the specialty insurance marketplace. The consolidated balance sheet as of June 30, 2016, the related consolidated statements of income and comprehensive income (loss) for the quarters and six months ended June 30, 2016 and 2015, and the consolidated statements of changes in equity and cash flows for the six months ended June 30, 2016 and 2015 are unaudited. In the opinion of management, all adjustments necessary for fair presentation of such consolidated financial statements have been included. Such adjustments consist only of normal, recurring items. Interim results are not necessarily indicative of results of operations for the entire year. The consolidated balance sheet as of December 31, 2015 was derived from Markel Corporation's audited annual consolidated financial statements. The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) and include the accounts of Markel Corporation and its consolidated subsidiaries, as well as any variable interest entities (VIEs) that meet the requirements for consolidation (the Company). All significant intercompany balances and transactions have been eliminated in consolidation. The Company consolidates the results of its Markel Ventures subsidiaries on a one-month lag. Certain prior year amounts have been reclassified to conform to the current presentation. The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements. The consolidated financial statements and notes are presented as permitted by Form 10-Q and do not contain certain information included in the Company's annual consolidated financial statements and notes. In addition to the policies set forth below, readers are urged to review the Company's 2015 Annual Report on Form 10-K for a more complete description of the Company's business and accounting policies. b) Variable Interest Entities. The Company determines whether it has relationships with entities defined as VIEs in accordance with Accounting Standards Codification (ASC) Topic 810, Consolidation. Under this guidance, a VIE is consolidated by the variable interest holder that is determined to be the primary beneficiary. An entity in which the Company holds a variable interest is a VIE if any of the following conditions exist: (a) the total equity investment at risk is not sufficient to permit the entity to finance its activities without additional subordinated financial support, (b) as a group, the holders of equity investment at risk lack either the direct or indirect ability through voting rights or similar rights to make decisions about an entity's activities that most significantly impact the entity’s economic performance or the obligation to absorb the expected losses or right to receive the expected residual returns, or (c) the voting rights of some investors are disproportionate to their obligation to absorb the expected losses of the entity, their rights to receive the expected residual returns of the entity, or both and substantially all of the entity's activities either involve or are conducted on behalf of an investor with disproportionately few voting rights. The primary beneficiary is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (a) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (b) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE. The Company determines whether an entity is a VIE at the inception of our variable interest in the entity and upon the occurrence of certain reconsideration events. The Company continually reassesses whether it is the primary beneficiary of VIEs in which it holds a variable interest. c) Revenue Recognition. Investment Management and Performance Fees Investment management fee income is recognized over the period in which investment management services are provided and is calculated and billed monthly based on the net asset value of the accounts managed. Performance fee arrangements entitle the Company to participate, on a fixed-percentage basis, in any net income generated in excess of an agreed-upon threshold as established by the underlying investment management agreements. In general, net income is calculated at the end of each calendar year and performance fees are payable annually. Following the preferred method identified in the ASC Topic 605, Revenue Recognition, such performance fee income is recorded at the conclusion of the contractual performance period, when all contingencies are resolved.

Summary of Significant Accounting Policies

a) Basis of Presentation. Markel Corporation is a diverse financial holding company serving a variety of niche markets. Markel Corporation's principal business markets and underwrites specialty insurance products and programs. Through its wholly-owned subsidiary, Markel Ventures, Inc. (Markel Ventures), Markel Corporation also owns interests in various industrial and service businesses that operate outside of the specialty insurance marketplace.

The consolidated balance sheet as of June 30, 2016, the related consolidated statements of income and comprehensive income (loss) for the quarters and six months ended June 30, 2016 and 2015, and the consolidated statements of changes in equity and cash flows for the six months ended June 30, 2016 and 2015 are unaudited. In the opinion of management, all adjustments necessary for fair presentation of such consolidated financial statements have been included. Such adjustments consist only of normal, recurring items. Interim results are not necessarily indicative of results of operations for the entire year. The consolidated balance sheet as of December 31, 2015 was derived from Markel Corporation's audited annual consolidated financial statements.

The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (U.S. GAAP) and include the accounts of Markel Corporation and its consolidated subsidiaries, as well as any variable interest entities (VIEs) that meet the requirements for consolidation (the Company). All significant intercompany balances and transactions have been eliminated in consolidation. The Company consolidates the results of its Markel Ventures subsidiaries on a one-month lag. Certain prior year amounts have been reclassified to conform to the current presentation.

The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements.

The consolidated financial statements and notes are presented as permitted by Form 10-Q and do not contain certain information included in the Company's annual consolidated financial statements and notes. In addition to the policies set forth below, readers are urged to review the Company's 2015 Annual Report on Form 10-K for a more complete description of the Company's business and accounting policies.

b) Variable Interest Entities. The Company determines whether it has relationships with entities defined as VIEs in accordance with Accounting Standards Codification (ASC) Topic 810, Consolidation. Under this guidance, a VIE is consolidated by the variable interest holder that is determined to be the primary beneficiary.

An entity in which the Company holds a variable interest is a VIE if any of the following conditions exist: (a) the total equity investment at risk is not sufficient to permit the entity to finance its activities without additional subordinated financial support, (b) as a group, the holders of equity investment at risk lack either the direct or indirect ability through voting rights or similar rights to make decisions about an entity's activities that most significantly impact the entity’s economic performance or the obligation to absorb the expected losses or right to receive the expected residual returns, or (c) the voting rights of some investors are disproportionate to their obligation to absorb the expected losses of the entity, their rights to receive the expected residual returns of the entity, or both and substantially all of the entity's activities either involve or are conducted on behalf of an investor with disproportionately few voting rights.

The primary beneficiary is defined as the variable interest holder that is determined to have the controlling financial interest as a result of having both (a) the power to direct the activities of a VIE that most significantly impact the economic performance of the VIE and (b) the obligation to absorb losses or right to receive benefits from the VIE that could potentially be significant to the VIE.

The Company determines whether an entity is a VIE at the inception of our variable interest in the entity and upon the occurrence of certain reconsideration events. The Company continually reassesses whether it is the primary beneficiary of VIEs in which it holds a variable interest.

c) Revenue Recognition.

Investment Management and Performance Fees

Investment management fee income is recognized over the period in which investment management services are provided and is calculated and billed monthly based on the net asset value of the accounts managed. Performance fee arrangements entitle the Company to participate, on a fixed-percentage basis, in any net income generated in excess of an agreed-upon threshold as established by the underlying investment management agreements. In general, net income is calculated at the end of each calendar year and performance fees are payable annually. Following the preferred method identified in the ASC Topic 605, Revenue Recognition, such performance fee income is recorded at the conclusion of the contractual performance period, when all contingencies are resolved.