Contingencies	3 Months Ended
Mar. 31, 2019
Loss Contingency [Abstract]
Contingencies	Contingencies a) Late in the fourth quarter of 2018, the Company was contacted by and received inquiries from the U.S. Department of Justice, U.S. Securities and Exchange Commission and Bermuda Monetary Authority (collectively, Governmental Authorities) into loss reserves recorded in late 2017 and early 2018 at Markel CATCo Re (the Markel CATCo Inquiries), an unconsolidated subsidiary managed by MCIM. As a result, the Company engaged outside counsel to conduct an internal review. The internal review was completed in April 2019 and found no evidence that MCIM personnel acted in bad faith in exercising business judgment in the setting of reserves and making related disclosures during late 2017 and early 2018. The Company’s outside counsel has met with the Governmental Authorities and reported the findings from the internal review. The Markel CATCo Inquiries are ongoing. The Company cannot currently predict the duration, scope or result of the Markel CATCo Inquiries. During the internal review, the Company discovered violations of Markel policies by two senior executives of MCIM. As a result, these two executives are no longer with the Company (the MCIM Executive Departures). Between January 11, 2019 and March 7, 2019, several related putative class actions were filed in the U.S. District Court for the Southern District of New York against Markel Corporation and certain present or former officers and directors alleging violations of the federal securities laws relating to the matters that are the subject of the Markel CATCo Inquiries (the Markel Securities Litigation). Plaintiffs seek to represent a class of persons or entities that purchased Markel securities between July 26, 2017 and December 6, 2018. The actions have been consolidated. The Company believes that the claims against it are without merit. The Company further believes any material loss resulting from the suit to be remote. On February 21, 2019, Anthony Belisle and Alissa Fredricks, the two senior executives who are no longer with MCIM, each separately filed suit against MCIM and Markel Corporation, which suits were amended on March 29, 2019 and March 28, 2019, respectively (the MCIM Executive Suits). As amended, the complaints allege claims for, among other things, breach of contract, defamation, invasion of privacy, indemnification, intentional interference with contractual relations and deceptive and unfair acts. Mr. Belisle's complaint seeks relief including payment of $66.0 million in incentive compensation and Ms. Fredricks's complaint seeks relief including payment of $7.5 million in incentive compensation. In addition, both seek consequential damages, damages for emotional distress and injury to reputation, statutory interest, exemplary damages and attorneys’ fees, among other things. Mr. Belisle's complaint further seeks enhanced compensatory damages. The Company believes that all claims are without merit. The Company further believes any material loss resulting from the suits to be remote. The Markel CATCo Inquiries, Markel Securities Litigation, MCIM Executive Departures and MCIM Executive Suits, as well as other related matters of which the Company is currently unaware, could result in additional claims, litigation, investigations, enforcement actions or proceedings. For example, additional litigation may be filed by investors in the Markel CATCo Funds. The Company also could become subject to increased regulatory scrutiny, investigations or proceedings in any of the jurisdictions where it operates. If any regulatory authority takes action against the Company or the Company enters into an agreement to settle a matter, the Company may incur sanctions or be required to pay substantial fines or implement remedial measures that could prove costly or disruptive to its businesses and operations. Costs associated with the Company's internal review, including legal and investigation costs, as well as legal costs incurred in connection with any existing or future litigation, are being expensed as incurred. An unfavorable outcome in one or more of these matters, and others the Company cannot anticipate, could have a material adverse effect on the Company’s results of operations and financial condition. In addition, the Company may take further steps to support the Markel CATCo operations, including steps to mitigate potential risks or liabilities that may arise from the Markel CATCo Inquiries and related developments and some of those steps may have a material impact on the Company’s results of operations or financial condition. Even if an unfavorable outcome does not materialize, these matters, and actions the Company may take in response, could have an adverse impact on the Company’s reputation and result in substantial expense and disruption. In December 2018, investors in the Markel CATCo Funds were offered an additional redemption opportunity (the Special Redemption). Under the Special Redemption, investors in the Markel CATCo Funds were offered the option, through March 29, 2019, to redeem any or all shares held as of June 30, 2019. However, for (1) shares that have been restricted following the occurrence of catastrophic loss events for which uncertainty still exists around the ultimate incurred losses on the underlying reinsurance contracts at Markel CATCo Re and (2) shares that support insurance contracts that are still exposed to future underwriting risk, such amounts will not be redeemed until all remaining exposures are fully settled or released by cedents, which could take up to four years. Through both the Special Redemption and the annual redemption for January 1, 2019, 73% of investors, comprising 91% of net assets under management as of March 31, 2019, elected to redeem their shares in the Markel CATCo Funds. Payment for the redemptions of shares is an obligation of the Markel CATCo Funds, not Markel Corporation or its subsidiaries. b) The Company has reviewed events at one of its Markel Ventures products businesses. Since becoming aware of a matter late in the first quarter of 2018 related to the business's manufacture of products, the Company has conducted an investigation, reviewed the business's operations and developed remediation plans. Upon completion of its review during 2018, the Company accrued an expense of $33.5 million in its results of operations. This amount represented management’s best estimate of amounts considered probable including: remediation costs associated with the manufacture of products, costs associated with the investigation of this matter, a write down of inventory on hand and settlement costs related to pre-existing litigation. Final resolution of this matter could ultimately result in additional remediation and other costs, the amount of which cannot be estimated at this time, but which could have a material impact on the Company’s income before income taxes. However, management does not expect this matter ultimately will have a material adverse effect on the Company’s results of operations or financial condition. If a determination is made that additional costs associated with this matter are considered probable, these additional costs will be recognized as an expense in the Company's results of operations. As of March 31, 2019, $26.4 million remained accrued for ongoing remediation efforts. In addition, contingencies arise in the normal course of the Company's operations and are not expected to have a material impact on the Company's financial condition or results of operations.

Contingencies

a) Late in the fourth quarter of 2018, the Company was contacted by and received inquiries from the U.S. Department of Justice, U.S. Securities and Exchange Commission and Bermuda Monetary Authority (collectively, Governmental Authorities) into loss reserves recorded in late 2017 and early 2018 at Markel CATCo Re (the Markel CATCo Inquiries), an unconsolidated subsidiary managed by MCIM. As a result, the Company engaged outside counsel to conduct an internal review.

The internal review was completed in April 2019 and found no evidence that MCIM personnel acted in bad faith in exercising business judgment in the setting of reserves and making related disclosures during late 2017 and early 2018. The Company’s outside counsel has met with the Governmental Authorities and reported the findings from the internal review. The Markel CATCo Inquiries are ongoing. The Company cannot currently predict the duration, scope or result of the Markel CATCo Inquiries.

During the internal review, the Company discovered violations of Markel policies by two senior executives of MCIM. As a result, these two executives are no longer with the Company (the MCIM Executive Departures).

Between January 11, 2019 and March 7, 2019, several related putative class actions were filed in the U.S. District Court for the Southern District of New York against Markel Corporation and certain present or former officers and directors alleging violations of the federal securities laws relating to the matters that are the subject of the Markel CATCo Inquiries (the Markel Securities Litigation). Plaintiffs seek to represent a class of persons or entities that purchased Markel securities between July 26, 2017 and December 6, 2018. The actions have been consolidated. The Company believes that the claims against it are without merit. The Company further believes any material loss resulting from the suit to be remote.

On February 21, 2019, Anthony Belisle and Alissa Fredricks, the two senior executives who are no longer with MCIM, each separately filed suit against MCIM and Markel Corporation, which suits were amended on March 29, 2019 and March 28, 2019, respectively (the MCIM Executive Suits). As amended, the complaints allege claims for, among other things, breach of contract, defamation, invasion of privacy, indemnification, intentional interference with contractual relations and deceptive and unfair acts. Mr. Belisle's complaint seeks relief including payment of $66.0 million in incentive compensation and Ms. Fredricks's complaint seeks relief including payment of $7.5 million in incentive compensation. In addition, both seek consequential damages, damages for emotional distress and injury to reputation, statutory interest, exemplary damages and attorneys’ fees, among other things. Mr. Belisle's complaint further seeks enhanced compensatory damages. The Company believes that all claims are without merit. The Company further believes any material loss resulting from the suits to be remote.

The Markel CATCo Inquiries, Markel Securities Litigation, MCIM Executive Departures and MCIM Executive Suits, as well as other related matters of which the Company is currently unaware, could result in additional claims, litigation, investigations, enforcement actions or proceedings. For example, additional litigation may be filed by investors in the Markel CATCo Funds. The Company also could become subject to increased regulatory scrutiny, investigations or proceedings in any of the jurisdictions where it operates. If any regulatory authority takes action against the Company or the Company enters into an agreement to settle a matter, the Company may incur sanctions or be required to pay substantial fines or implement remedial measures that could prove costly or disruptive to its businesses and operations. Costs associated with the Company's internal review, including legal and investigation costs, as well as legal costs incurred in connection with any existing or future litigation, are being expensed as incurred.

An unfavorable outcome in one or more of these matters, and others the Company cannot anticipate, could have a material adverse effect on the Company’s results of operations and financial condition. In addition, the Company may take further steps to support the Markel CATCo operations, including steps to mitigate potential risks or liabilities that may arise from the Markel CATCo Inquiries and related developments and some of those steps may have a material impact on the Company’s results of operations or financial condition. Even if an unfavorable outcome does not materialize, these matters, and actions the Company may take in response, could have an adverse impact on the Company’s reputation and result in substantial expense and disruption.

In December 2018, investors in the Markel CATCo Funds were offered an additional redemption opportunity (the Special Redemption). Under the Special Redemption, investors in the Markel CATCo Funds were offered the option, through March 29, 2019, to redeem any or all shares held as of June 30, 2019. However, for (1) shares that have been restricted following the occurrence of catastrophic loss events for which uncertainty still exists around the ultimate incurred losses on the underlying reinsurance contracts at Markel CATCo Re and (2) shares that support insurance contracts that are still exposed to future underwriting risk, such amounts will not be redeemed until all remaining exposures are fully settled or released by cedents, which could take up to four years. Through both the Special Redemption and the annual redemption for January 1, 2019, 73% of investors, comprising 91% of net assets under management as of March 31, 2019, elected to redeem their shares in the Markel CATCo Funds. Payment for the redemptions of shares is an obligation of the Markel CATCo Funds, not Markel Corporation or its subsidiaries.

b) The Company has reviewed events at one of its Markel Ventures products businesses. Since becoming aware of a matter late in the first quarter of 2018 related to the business's manufacture of products, the Company has conducted an investigation, reviewed the business's operations and developed remediation plans. Upon completion of its review during 2018, the Company accrued an expense of $33.5 million in its results of operations. This amount represented management’s best estimate of amounts considered probable including: remediation costs associated with the manufacture of products, costs associated with the investigation of this matter, a write down of inventory on hand and settlement costs related to pre-existing litigation.

Final resolution of this matter could ultimately result in additional remediation and other costs, the amount of which cannot be estimated at this time, but which could have a material impact on the Company’s income before income taxes. However, management does not expect this matter ultimately will have a material adverse effect on the Company’s results of operations or financial condition. If a determination is made that additional costs associated with this matter are considered probable, these additional costs will be recognized as an expense in the Company's results of operations. As of March 31, 2019, $26.4 million remained accrued for ongoing remediation efforts.

In addition, contingencies arise in the normal course of the Company's operations and are not expected to have a material impact on the Company's financial condition or results of operations.