XML 57 R44.htm IDEA: XBRL DOCUMENT
v3.20.2

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 USD ($) | Jun. 30, 2019 USD ($) | Jun. 30, 2020 USD ($) segment | Jun. 30, 2019 USD ($)
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Number of reportable ongoing underwriting segments | segment |  |  |  |  | 2 |  |  |
Gross premium volume | $ 2,373,192 |  | $ 2,247,147 |  | $ 4,696,016 |  | $ 4,502,189 |
Net written premiums | 1,456,395 |  | 1,305,638 |  | 3,102,873 |  | 2,782,731 |
Earned premiums | 1,360,174 |  | 1,199,461 |  | 2,690,883 |  | 2,403,438 |
Losses and loss adjustment expenses, current accident year | (877,364) |  | (796,712) |  | (2,057,729) |  | (1,554,682) |
Losses and loss adjustment expenses, prior accident year | 164,148 |  | 118,592 |  | 268,165 |  | 188,816 |
Amortization of policy acquisition costs | (302,195) |  | (263,065) |  | (598,006) |  | (524,892) |
Other operating expenses | (187,167) |  | (199,251) |  | (386,519) |  | (392,636) |
Underwriting profit (loss) | 157,596 |  | 59,025 |  | (83,206) |  | 120,044 |
Net investment income | 95,615 |  | 111,831 |  | 183,858 |  | 226,013 |
Net investment gains (losses) | 911,243 |  | 425,653 |  | (770,198) |  | 1,037,844 |
Products revenues | 423,581 |  | 501,676 |  | 775,742 |  | 850,470 |
Services and other revenues | 341,402 |  | 200,495 |  | 587,396 |  | 393,839 |
Products expenses | (364,483) |  | (425,138) |  | (678,554) |  | (744,564) |
Services and other expenses | (284,940) |  | (170,796) |  | (502,496) |  | (345,402) |
Amortization of intangible assets | (37,754) | [1] | (36,300) | [2] | (75,612) | [3] | (76,968) | [4]
Segment profit (loss) | 1,242,260 |  | 666,446 |  | (563,070) |  | 1,461,276 |
Interest expense | (45,427) |  | (41,267) |  | (90,457) |  | (81,557) |
Net foreign exchange gains (losses) | (21,460) |  | 25,015 |  | 56,841 |  | 3,151 |
Income (Loss) before income taxes | $ 1,175,373 |  | $ 650,194 |  | $ (596,686) |  | $ 1,382,870 |
U.S. GAAP combined ratio | 88.00% | [5] | 95.00% | [6] | 103.00% | [7] | 95.00% | [8]
Insurance [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Gross premium volume | $ 1,553,436 |  | $ 1,368,348 |  | $ 2,968,147 |  | $ 2,561,196 |
Net written premiums | 1,267,976 |  | 1,126,170 |  | 2,463,713 |  | 2,124,528 |
Earned premiums | 1,120,151 |  | 991,269 |  | 2,227,002 |  | 1,964,996 |
Losses and loss adjustment expenses, current accident year | (730,201) |  | (657,372) |  | (1,736,836) |  | (1,275,870) |
Losses and loss adjustment expenses, prior accident year | 151,205 |  | 101,721 |  | 267,337 |  | 174,295 |
Amortization of policy acquisition costs | (238,784) |  | (208,609) |  | (478,204) |  | (408,608) |
Other operating expenses | (167,298) |  | (179,432) |  | (350,600) |  | (355,153) |
Underwriting profit (loss) | 135,073 |  | 47,577 |  | (71,301) |  | 99,660 |
Net investment income | 0 |  | 0 |  | 0 |  | 0 |
Net investment gains (losses) | 0 |  | 0 |  | 0 |  | 0 |
Products revenues | 0 |  | 0 |  | 0 |  | 0 |
Services and other revenues | 0 |  | 0 |  | 0 |  | 0 |
Products expenses | 0 |  | 0 |  | 0 |  | 0 |
Services and other expenses | 0 |  | 0 |  | 0 |  | 0 |
Amortization of intangible assets | 0 | [1] | 0 | [2] | 0 | [3] | 0 | [4]
Segment profit (loss) | $ 135,073 |  | $ 47,577 |  | $ (71,301) |  | $ 99,660 |
U.S. GAAP combined ratio | 88.00% | [5] | 95.00% | [6] | 103.00% | [7] | 95.00% | [8]
Reinsurance [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Gross premium volume | $ 223,277 |  | $ 223,381 |  | $ 736,463 |  | $ 736,758 |
Net written premiums | 188,830 |  | 178,802 |  | 641,579 |  | 657,769 |
Earned premiums | 240,555 |  | 207,728 |  | 466,515 |  | 438,238 |
Losses and loss adjustment expenses, current accident year | (147,163) |  | (139,340) |  | (320,893) |  | (278,812) |
Losses and loss adjustment expenses, prior accident year | 12,280 |  | 18,190 |  | (1,632) |  | 6,895 |
Amortization of policy acquisition costs | (63,411) |  | (54,456) |  | (119,802) |  | (116,284) |
Other operating expenses | (17,506) |  | (23,306) |  | (33,392) |  | (37,865) |
Underwriting profit (loss) | 24,755 |  | 8,816 |  | (9,204) |  | 12,172 |
Net investment income | 0 |  | 0 |  | 0 |  | 0 |
Net investment gains (losses) | 0 |  | 0 |  | 0 |  | 0 |
Products revenues | 0 |  | 0 |  | 0 |  | 0 |
Services and other revenues | 0 |  | 0 |  | 0 |  | 0 |
Products expenses | 0 |  | 0 |  | 0 |  | 0 |
Services and other expenses | 0 |  | 0 |  | 0 |  | 0 |
Amortization of intangible assets | 0 | [1] | 0 | [2] | 0 | [3] | 0 | [4]
Segment profit (loss) | $ 24,755 |  | $ 8,816 |  | $ (9,204) |  | $ 12,172 |
U.S. GAAP combined ratio | 90.00% | [5] | 96.00% | [6] | 102.00% | [7] | 97.00% | [8]
Investing [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Gross premium volume | $ 0 |  | $ 0 |  | $ 0 |  | $ 0 |
Net written premiums | 0 |  | 0 |  | 0 |  | 0 |
Earned premiums | 0 |  | 0 |  | 0 |  | 0 |
Losses and loss adjustment expenses, current accident year | 0 |  | 0 |  | 0 |  | 0 |
Losses and loss adjustment expenses, prior accident year | 0 |  | 0 |  | 0 |  | 0 |
Amortization of policy acquisition costs | 0 |  | 0 |  | 0 |  | 0 |
Other operating expenses | 0 |  | 0 |  | 0 |  | 0 |
Underwriting profit (loss) | 0 |  | 0 |  | 0 |  | 0 |
Net investment income | 95,561 |  | 111,633 |  | 183,620 |  | 225,563 |
Net investment gains (losses) | 911,243 |  | 425,653 |  | (770,198) |  | 1,037,844 |
Products revenues | 0 |  | 0 |  | 0 |  | 0 |
Services and other revenues | 0 |  | 0 |  | 0 |  | 0 |
Products expenses | 0 |  | 0 |  | 0 |  | 0 |
Services and other expenses | 0 |  | 0 |  | 0 |  | 0 |
Amortization of intangible assets | 0 | [1] | 0 | [2] | 0 | [3] | 0 | [4]
Segment profit (loss) | 1,006,804 |  | 537,286 |  | (586,578) |  | 1,263,407 |
Markel Ventures [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Gross premium volume | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Net written premiums | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Earned premiums | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Losses and loss adjustment expenses, current accident year | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Losses and loss adjustment expenses, prior accident year | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Amortization of policy acquisition costs | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Other operating expenses | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Underwriting profit (loss) | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Net investment income | 54 | [9] | 198 | [10] | 238 | [11] | 450 | [12]
Net investment gains (losses) | 0 | [9] | 0 | [10] | 0 | [11] | 0 | [12]
Products revenues | 423,581 | [9] | 501,676 | [10] | 775,742 | [11] | 850,470 | [12]
Services and other revenues | 254,504 | [9] | 115,311 | [10] | 413,380 | [11] | 221,280 | [12]
Products expenses | (364,483) | [9] | (425,138) | [10] | (678,554) | [11] | (744,564) | [12]
Services and other expenses | (222,656) | [9] | (99,860) | [10] | (366,208) | [11] | (194,730) | [12]
Amortization of intangible assets | (11,596) | [1],[9] | (10,510) | [2],[10] | (23,437) | [3],[11] | (21,317) | [4],[12]
Segment profit (loss) | 79,404 |  | 81,677 | [10] | 121,161 | [11] | 111,589 | [12]
Depreciation | 14,300 |  | 13,500 |  | 28,100 | [11] | 27,500 | [12]
Underwriting Segments [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Amortization of intangible assets | 10,700 |  | 9,800 |  | 21,100 |  | 19,700 |
Other [Member] |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |
Gross premium volume | 596,479 | [13] | 655,418 | [14] | 991,406 | [15] | 1,204,235 | [16]
Net written premiums | (411) | [13] | 666 | [14] | (2,419) | [15] | 434 | [16]
Earned premiums | (532) | [13] | 464 | [14] | (2,634) | [15] | 204 | [16]
Losses and loss adjustment expenses, current accident year | 0 | [13] | 0 | [14] | 0 | [15] | 0 | [16]
Losses and loss adjustment expenses, prior accident year | 663 | [13] | (1,319) | [14] | 2,460 | [15] | 7,626 | [16]
Amortization of policy acquisition costs | 0 | [13] | 0 | [14] | 0 | [15] | 0 | [16]
Other operating expenses | (2,363) | [13] | 3,487 | [14] | (2,527) | [15] | 382 | [16]
Underwriting profit (loss) | (2,232) | [13] | 2,632 | [14] | (2,701) | [15] | 8,212 | [16]
Net investment income | 0 | [13] | 0 | [14] | 0 | [15] | 0 | [16]
Net investment gains (losses) | 0 | [13] | 0 | [14] | 0 | [15] | 0 | [16]
Products revenues | 0 | [13] | 0 | [14] | 0 | [15] | 0 | [16]
Services and other revenues | 86,898 | [13] | 85,184 | [14] | 174,016 | [15] | 172,559 | [16]
Products expenses | 0 | [13] | 0 | [14] | 0 | [15] | 0 | [16]
Services and other expenses | (62,284) | [13] | (70,936) | [14] | (136,288) | [15] | (150,672) | [16]
Amortization of intangible assets | (26,158) | [1],[13] | (25,790) | [2],[14] | (52,175) | [3],[15] | (55,651) | [4],[16]
Segment profit (loss) | $ (3,776) | [13] | $ (8,910) | [14] | $ (17,148) | [15] | $ (25,552) | [12]
U.S. GAAP combined ratio - not meaniningful | NM | [5],[13],[17] | NM | [6],[14],[18] | NM | [7],[15],[19] | NM | [8],[16],[20]
[1] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments.
[2] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments.
[3] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments.
[4] | Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments.
[5] | The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.
[6] | The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.
[7] | The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.
[8] | The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.
[9] | Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $14.3 million for the quarter ended June 30, 2020.
[10] | Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $13.5 million for the quarter ended June 30, 2019.
[11] | Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $28.1 million for the six months ended June 30, 2020.
[12] | Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $27.5 million for the six months ended June 30, 2019.
[13] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $10.7 million for the quarter ended June 30, 2020, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments.
[14] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $9.8 million for the quarter ended June 30, 2019, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments.
[15] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $21.1 million for the six months ended June 30, 2020, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments.
[16] | Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $19.7 million for the six months ended June 30, 2019, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments.
[17] | NM - Ratio is not meaningful
[18] | NM - Ratio is not meaningful
[19] | NM - Ratio is not meaningful
[20] | NM - Ratio is not meaningful

X
- Definition The net gains or losses on investments during the period, also including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity. + References No definition available. + Details
Name: | mkl_NetInvestmentGainsLosses
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The number of segments reported by the entity through which our ongoing underwriting operations are conducted. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | mkl_NumberOfReportableOngoingUnderwritingSegments
Namespace Prefix: | mkl_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Products Revenues + References No definition available. + Details
Name: | mkl_ProductsRevenues
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Products expenses + References No definition available. + Details
Name: | mkl_Productsexpenses
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Services and other expenses + References No definition available. + Details
Name: | mkl_Servicesandotherexpenses
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Services and other revenues + References No definition available. + Details
Name: | mkl_Servicesandotherrevenues
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related settlement costs, including amounts related to liabilities not classified as unpaid losses and loss adjustment expenses. + References No definition available. + Details
Name: | mkl_SupplementalInfoForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpenseIncludingAmountsRelatedToLiabilitiesNotIncludedInUnpaidLossesAndLAE
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of profit (loss) recognized by the reportable segment or the company's other operations which are not included in a reportable segment. + References No definition available. + Details
Name: | mkl_TotalProfitLoss
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition US GAAP combined ratio - not meaningful + References No definition available. + Details
Name: | mkl_USGAAPcombinedrationotmeaningful
Namespace Prefix: | mkl_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Earned premiums less incurred losses, loss adjustment expenses and other underwriting, acquisition and insurance expenses. + References No definition available. + Details
Name: | mkl_UnderwritingProfitLoss
Namespace Prefix: | mkl_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 + Details
Name: | us-gaap_AmortizationOfIntangibleAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Ratio of non-life losses and loss expenses, non-life acquisition expenses and non-life general and administrative expenses, to non-life net premiums earned. + References No definition available. + Details
Name: | us-gaap_CombinedRatio
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of amortization expense (reversal of expense) for deferred policy acquisition costs. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 55 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=117418976&loc=d3e11522-158419 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 45 -Paragraph 2 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6480726&loc=d3e6691-158385 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=117419843&loc=SL117420844-207641 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(7)(a)) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 50 -Paragraph 2B -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117419109&loc=SL117422543-158416 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35755530&loc=d3e11264-158415 + Details
Name: | us-gaap_DeferredPolicyAcquisitionCostAmortizationExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585 + Details
Name: | us-gaap_Depreciation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount before tax of foreign currency transaction realized gain (loss) recognized in the income statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109240200&loc=d3e30690-110894 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109240200&loc=d3e30700-110894 + Details
Name: | us-gaap_ForeignCurrencyTransactionGainLossRealized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 20 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=68072869&loc=d3e41242-110953 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(10)) -URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(8)) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(15)) -URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260 + Details
Name: | us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of the cost of borrowed funds accounted for as interest expense. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (210.5-03(11)) -URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.9) -URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260 + Details
Name: | us-gaap_InterestExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 + Details
Name: | us-gaap_NetInvestmentIncome
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Costs incurred during the period, such as those relating to general administration and policy maintenance that do not vary with and are not primarily related to the acquisition or renewal of insurance contracts. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.7) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 720 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35755714&loc=d3e28434-158551 + Details
Name: | us-gaap_OtherUnderwritingExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(1)) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17(Column E)) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)(c)) -URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
Name: | us-gaap_PremiumsEarnedNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of direct and assumed premiums written. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
Name: | us-gaap_PremiumsWrittenGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums written. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
Name: | us-gaap_PremiumsWrittenNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mkl_InsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mkl_ReinsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mkl_InvestingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mkl_MarkelVenturesOperationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mkl_UnderwritingSegmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mkl_OtherMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |