Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Jun. 30, 2020
Loss Contingency [Abstract]
Commitments and Contingencies	Commitments and 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 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. On February 21, 2019, Anthony Belisle, one of the two senior executives that is no longer with MCIM, filed suit against MCIM and Markel Corporation, which suit was amended on March 29, 2019. As amended, Mr. Belisle's complaint alleged claims for, among other things, breach of contract, defamation, invasion of privacy, indemnification, intentional interference with contractual relations and deceptive and unfair acts and sought relief of, among other things, $66.0 million in incentive compensation, enhanced compensatory damages, consequential damages, damages for emotional distress and injury to reputation, exemplary damages and attorneys' fees. In June 2019, MCIM, Markel Corporation, and Mr. Belisle agreed to commence binding arbitration to finally, fully and confidentially resolve the claims and counterclaims alleged in the action, and the Belisle suit was dismissed with prejudice in July 2019. The arbitrators have been selected, the arbitration proceeding has commenced and the arbitration hearing has been scheduled to begin in August 2020. In late July, the parties commenced settlement discussions and reached an agreement in principal on a mutually acceptable settlement amount. The Company expects that a settlement agreement will be entered into and the settlement amount will be recorded and reflected in the Company’s net income in the third quarter of 2020. The settlement amount is not material to the Company’s consolidated results of operations or financial condition. In July 2019, MCIM announced it would cease accepting new investments in the Markel CATCo Funds and would not write any new business in Markel CATCo Re. Both the Markel CATCo Funds and Markel CATCo Re have been placed into run-off, returning capital to investors as it becomes available. The process is expected to take approximately three years. The Markel CATCo Inquiries, as well as other matters related to or arising from the Markel CATCo Inquiries, including 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 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. b)Since becoming aware of a matter in the first quarter of 2018 related to the manufacturing of products at one of the Company's Markel Ventures businesses, the Company has conducted an investigation, reviewed the business's operations and developed remediation plans. Upon completion of its review during 2018, the Company recorded an expense of $33.5 million in its results of operations and began implementing remediation plans. The amount accrued 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. As of June 30, 2020, $20.2 million remained accrued for this matter. 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. c)In 2019, the Company established Lodgepine Capital Management Limited (Lodgepine), a new retrocessional insurance-linked securities fund manager in Bermuda. Lodgepine's initial product offering will be Lodgepine Fund Limited, a property catastrophe retrocessional investment fund, which the Company has been preparing to launch sometime in 2020. However, this timing has been impacted by the recent downturn in global market conditions, and corresponding impact on prospective investor capital allocation decisions. Subject to certain conditions, the Company has committed to invest up to $100 million in Lodgepine Fund Limited. d)On March 11, 2020, COVID-19, a novel coronavirus outbreak, was declared a pandemic by the World Health Organization. See note 16 for further details regarding potential impacts of COVID-19 on the Company's business. e)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.