XML 114 R89.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Unpaid Losses And Loss Adjustment Expenses (Ultimate Incurred Losses And Cumulative Paid Losses And Allocated Loss Adjustment Expenses, Net Of Reinsurance) (Details) | Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance | $ 15,087,702,000 |  |  |  |  |  |  |  |  |
Insurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 27,539,900,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 16,302,700,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for unpaid losses and loss adjustment expenses before 2014, net of reinsurance | 313,300,000 |  |  |  |  |  |  |  |  |
Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance | 11,550,516,000 |  |  |  |  |  |  |  |  |
Insurance [Member] | 2015 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 1,457,100,000 | $ 1,460,000,000 | $ 1,440,900,000 | $ 1,450,600,000 | $ 1,454,700,000 | $ 1,486,500,000 | $ 1,517,000,000 | $ 1,571,000,000 | $ 1,693,800,000 | $ 1,767,500,000
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 58,000,000.0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 88,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 1,344,700,000 | 1,327,300,000 | 1,291,700,000 | 1,259,200,000 | 1,208,400,000 | 1,141,300,000 | 1,032,900,000 | 870,200,000 | 660,000,000.0 | 320,700,000
Insurance [Member] | 2016 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 1,718,100,000 | 1,732,900,000 | 1,678,400,000 | 1,667,400,000 | 1,674,700,000 | 1,700,300,000 | 1,753,600,000 | 1,852,800,000 | 1,856,300,000 |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 77,200,000 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 100,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 1,529,800,000 | 1,479,600,000 | 1,425,500,000 | 1,350,300,000 | 1,262,800,000 | 1,158,200,000 | 973,700,000 | 746,200,000 | 369,800,000 |
Insurance [Member] | 2017 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 2,152,300,000 | 2,111,200,000 | 2,023,900,000 | 2,004,500,000 | 1,998,700,000 | 2,059,300,000 | 2,176,700,000 | 2,309,000,000 |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 124,600,000 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 140,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 1,909,500,000 | 1,839,600,000 | 1,739,800,000 | 1,619,200,000 | 1,462,000,000 | 1,274,300,000 | 982,700,000 | 434,900,000 |  |
Insurance [Member] | 2018 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 2,417,100,000 | 2,331,600,000 | 2,151,200,000 | 2,058,800,000 | 2,199,200,000 | 2,320,800,000 | 2,429,000,000 |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 177,800,000 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 193,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 2,017,400,000 | 1,856,500,000 | 1,671,600,000 | 1,494,900,000 | 1,281,900,000 | 1,017,400,000 | 490,700,000 |  |  |
Insurance [Member] | 2019 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 2,526,800,000 | 2,471,700,000 | 2,293,700,000 | 2,239,700,000 | 2,402,200,000 | 2,552,400,000 |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 206,900,000 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 228,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 2,104,400,000 | 1,910,900,000 | 1,576,400,000 | 1,262,900,000 | 991,100,000 | 524,100,000 |  |  |  |
Insurance [Member] | 2020 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 2,771,600,000 | 2,858,500,000 | 2,914,200,000 | 2,972,100,000 | 3,185,100,000 |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 434,300,000 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 183,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 2,033,800,000 | 1,772,500,000 | 1,515,700,000 | 1,148,500,000 | 568,100,000 |  |  |  |  |
Insurance [Member] | 2021 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 2,720,100,000 | 2,755,400,000 | 2,907,100,000 | 3,083,500,000 |  |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 531,000,000.0 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 149,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 1,751,100,000 | 1,357,500,000 | 985,800,000 | 473,400,000 |  |  |  |  |  |
Insurance [Member] | 2022 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 3,342,600,000 | 3,365,500,000 | 3,746,800,000 |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 1,098,300,000 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 159,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 1,564,100,000 | 1,059,900,000 | 484,500,000 |  |  |  |  |  |  |
Insurance [Member] | 2023 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 3,901,700,000 | 4,435,900,000 |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 1,802,500,000 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 169,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 1,396,600,000 | 596,900,000 |  |  |  |  |  |  |  |
Insurance [Member] | 2024 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 4,532,500,000 |  |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | $ 3,271,700,000 |  |  |  |  |  |  |  |  |
Cumulative number of reported claims | 149,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 651,300,000 |  |  |  |  |  |  |  |  |
Reinsurance [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 7,017,100,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 3,847,700,000 |  |  |  |  |  |  |  |  |
All outstanding liabilities for unpaid losses and loss adjustment expenses before 2014, net of reinsurance | 273,300,000 |  |  |  |  |  |  |  |  |
Total liabilities for unpaid losses and loss adjustment expenses, net of reinsurance | 3,442,663,000 |  |  |  |  |  |  |  |  |
Reinsurance [Member] | 2015 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 477,700,000 | 500,000,000.0 | 488,200,000 | 487,800,000 | 499,900,000 | 504,800,000 | 516,000,000.0 | 524,600,000 | 508,800,000 | 523,000,000.0
Total of incurred-but-not-reported liabilities, net of reinsurance | 56,600,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 388,600,000 | 375,600,000 | 359,500,000 | 342,800,000 | 323,200,000 | 298,600,000 | 251,600,000 | 201,000,000.0 | 130,300,000 | $ 63,300,000
Reinsurance [Member] | 2016 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 556,500,000 | 573,300,000 | 551,500,000 | 548,100,000 | 523,400,000 | 513,400,000 | 515,400,000 | 515,200,000 | 506,600,000 |
Total of incurred-but-not-reported liabilities, net of reinsurance | 30,100,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 475,700,000 | 451,600,000 | 418,000,000.0 | 377,900,000 | 344,400,000 | 292,700,000 | 236,400,000 | 166,700,000 | $ 78,600,000 |
Reinsurance [Member] | 2017 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 931,300,000 | 931,000,000.0 | 919,700,000 | 907,300,000 | 934,900,000 | 933,200,000 | 927,600,000 | 894,400,000 |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | 44,200,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 796,000,000.0 | 747,600,000 | 692,800,000 | 623,800,000 | 560,400,000 | 478,600,000 | 357,500,000 | $ 157,100,000 |  |
Reinsurance [Member] | 2018 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 790,100,000 | 821,000,000.0 | 758,100,000 | 762,500,000 | 757,400,000 | 764,900,000 | 743,000,000.0 |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | 82,200,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 613,900,000 | 543,600,000 | 474,400,000 | 404,400,000 | 334,900,000 | 235,100,000 | $ 86,900,000 |  |  |
Reinsurance [Member] | 2019 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 730,400,000 | 719,000,000.0 | 691,000,000.0 | 683,100,000 | 668,400,000 | 654,400,000 |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | 129,100,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 507,700,000 | 435,600,000 | 351,800,000 | 261,300,000 | 169,100,000 | $ 53,200,000 |  |  |  |
Reinsurance [Member] | 2020 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 765,200,000 | 762,800,000 | 741,000,000.0 | 730,500,000 | 678,100,000 |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | 230,100,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 463,000,000.0 | 381,800,000 | 308,700,000 | 202,900,000 | $ 93,200,000 |  |  |  |  |
Reinsurance [Member] | 2021 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 753,900,000 | 754,700,000 | 733,600,000 | 731,900,000 |  |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | 303,800,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 361,000,000.0 | 281,600,000 | 187,100,000 | $ 79,200,000 |  |  |  |  |  |
Reinsurance [Member] | 2022 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 616,400,000 | 601,900,000 | 661,100,000 |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | 413,400,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 138,400,000 | 66,600,000 | $ 24,100,000 |  |  |  |  |  |  |
Reinsurance [Member] | 2023 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 665,300,000 | 658,300,000 |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | 506,700,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | 79,500,000 | $ 27,100,000 |  |  |  |  |  |  |  |
Reinsurance [Member] | 2024 Accident Year [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Ultimate incurred losses and allocated loss adjustment expenses, net of reinsurance | 730,300,000 |  |  |  |  |  |  |  |  |
Total of incurred-but-not-reported liabilities, net of reinsurance | 674,300,000 |  |  |  |  |  |  |  |  |
Cumulative paid losses and allocated loss adjustment expenses, net of reinsurance | $ 23,900,000 |  |  |  |  |  |  |  |  |

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/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4E Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4D -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4D Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4B Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4B + Details
Name: | us-gaap_ClaimsDevelopmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after reinsurance, of paid claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4B + Details
Name: | us-gaap_ShortdurationInsuranceContractsCumulativePaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of incurred-but-not-reported (IBNR) liabilities plus expected development on reported claims, for claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4E Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4D -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4D + Details
Name: | us-gaap_ShortdurationInsuranceContractsIncurredButNotReportedIbnrClaimsLiabilityNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of incurred claims and allocated claim adjustment expense used in claims development for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4B + Details
Name: | us-gaap_ShortdurationInsuranceContractsIncurredClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts. Excludes unallocated claim adjustment expense. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4C -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4C Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4B + Details
Name: | us-gaap_ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Undiscounted amount, after reinsurance, of the liability for unpaid claims and allocated claim adjustment expense for short-duration insurance contracts for accident years not separately presented in claim development information. Excludes unallocated claim adjustment expense. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4B -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4B + Details
Name: | us-gaap_ShortdurationInsuranceContractsLiabilityForUnpaidClaimsAndAllocatedClaimAdjustmentExpenseNetNotSeparatelyPresented
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Cumulative number of reported claims for short-duration insurance contracts. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 4D -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-4D + Details
Name: | us-gaap_ShortdurationInsuranceContractsNumberOfReportedClaims
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2015Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortdurationInsuranceContractsAccidentYear2016Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractsAccidentYear2017Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractsAccidentYear2018Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2019Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2020Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2021Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2022Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2023Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShortdurationInsuranceContractsAccidentYearAxis=us-gaap_ShortDurationInsuranceContractAccidentYear2024Member
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: |