XML 72 R61.htm IDEA: XBRL DOCUMENT
v3.24.2

Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2024 | Jun. 30, 2023 | Dec. 31, 2023
Related Party Transaction [Line Items] |  |  |  |  |
Services and other revenues | $ 684,481 | $ 672,291 | $ 1,302,119 | $ 1,238,152 |
Premiums ceded | 2,433,351 | 1,580,492 | 4,141,713 | 2,798,726 |
Reinsurance recoverables | 9,756,660 |  | 9,756,660 |  | $ 9,235,501
Nephila Reinsurers [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Reinsurance recoverables | 687,100 |  | 687,100 |  | 794,300
Hagerty, Inc. [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Gross premium volume | 275,642 | 236,225 | 473,924 | 401,196 |
Premiums ceded | 211,052 | 181,841 | 363,737 | 306,469 |
Reinsurance recoverables | 239,400 |  | 239,400 |  | $ 214,800
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Services and other revenues | 21,800 | 20,800 | 41,100 | 30,600 |
Program services and other fronting [Member] | Nephila Reinsurers [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Gross premium volume | 741,700 | 297,400 | 1,100,000 | 534,300 |
Premiums ceded | 741,700 | $ 297,400 | 1,100,000 | $ 534,300 |
Industry Loss Warranties (ILW) Program |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Premiums ceded | 168,000 |  | 168,000 |  |
Industry Loss Warranties (ILW) Program | Nephila Reinsurers [Member] |  |  |  |  |
Related Party Transaction [Line Items] |  |  |  |  |
Gross premium volume | $ 168,000 |  | $ 168,000 |  |

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 of written premiums ceded to other entities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
Name: | us-gaap_CededPremiumsWritten
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of direct and assumed premiums written. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 605 -Topic 944 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
Name: | us-gaap_PremiumsWrittenGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after valuation allowance, recoverable under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, policy benefits and policy reserves. Excludes premiums paid under reinsurance contracts. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477363/944-310-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479838/944-20-50-5 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 45 -Paragraph 5 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477409/944-310-45-5 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 45 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477409/944-310-45-6 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 825 -Name Accounting Standards Codification -Section 50 -Paragraph 1B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477351/944-825-50-1B + Details
Name: | us-gaap_ReinsuranceRecoverablesOnPaidAndUnpaidLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 310 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 13 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481990/310-10-45-13 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(2)(c)(2)(i)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(2)(c)(2)(ii)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(2)(g)(3)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1 + Details
Name: | us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=mkl_NephilaReinsurersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=mkl_HagertyIncMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementOperatingActivitiesSegmentAxis=mkl_InsurancelinkedSecuritiesOperationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=mkl_UnconsolidatedEntitiesManagedByNephilaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementOperatingActivitiesSegmentAxis=mkl_ProgramServicesAndOtherFrontingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementOperatingActivitiesSegmentAxis=mkl_IndustryLossWarrantiesILWProgramMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |