XML 60 R35.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Investments (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract] |
Available-For-Sale Investments | a) The following tables summarize the Company's available-for-sale investments. Agency mortgage-backed securities include securities issued by U.S. government-sponsored enterprises and U.S. government agencies. The net unrealized holding gains (losses) in the tables below are presented before taxes.
| December 31, 2024
(dollars in thousands) | Amortized Cost |  | Gross Unrealized Holding Gains |  | Gross Unrealized Holding Losses |  | Estimated Fair Value
Fixed maturity securities: |  |  |  |  |  |  |
U.S. Treasury securities | $ | 5,147,365 |  |  | $ | 8,962 |  |  | $ | (68,469) |  |  | $ | 5,087,858 |
U.S. government-sponsored enterprises | 1,445,171 |  |  | 2,976 |  |  | (101,911) |  |  | 1,346,236 |
Obligations of states, municipalities and political subdivisions | 3,813,146 |  |  | 5,866 |  |  | (199,520) |  |  | 3,619,492 |
Foreign governments, agencies and supranationals | 2,909,561 |  |  | 4,264 |  |  | (207,302) |  |  | 2,706,523 |
Agency mortgage-backed securities | 2,771,589 |  |  | 2,096 |  |  | (123,872) |  |  | 2,649,813 |
Non-agency mortgage-backed securities | 122,373 |  |  | — |  |  | (4,343) |  |  | 118,030 |
Corporate and university bonds | 248,518 |  |  | 76 |  |  | (31,007) |  |  | 217,587 |
Total fixed maturity securities | 16,457,723 |  |  | 24,240 |  |  | (736,424) |  |  | 15,745,539 |
Short-term investments | 2,530,941 |  |  | 548 |  |  | (6,579) |  |  | 2,524,910 |
Investments, available-for-sale | $ | 18,988,664 |  |  | $ | 24,788 |  |  | $ | (743,003) |  |  | $ | 18,270,449 |
| December 31, 2023
(dollars in thousands) | Amortized Cost |  | Gross Unrealized Holding Gains |  | Gross Unrealized Holding Losses |  | Estimated Fair Value
Fixed maturity securities: |  |  |  |  |  |  |
U.S. Treasury securities | $ | 3,811,293 |  |  | $ | 35,824 |  |  | $ | (62,404) |  |  | $ | 3,784,713 |
U.S. government-sponsored enterprises | 1,225,426 |  |  | 7,292 |  |  | (89,904) |  |  | 1,142,814 |
Obligations of states, municipalities and political subdivisions | 4,196,096 |  |  | 14,787 |  |  | (181,578) |  |  | 4,029,305 |
Foreign governments, agencies and supranationals | 2,554,874 |  |  | 34,352 |  |  | (142,008) |  |  | 2,447,218 |
Agency mortgage-backed securities | 2,507,682 |  |  | 8,939 |  |  | (135,611) |  |  | 2,381,010 |
Non-agency mortgage-backed securities | 355,673 |  |  | — |  |  | (22,603) |  |  | 333,070 |
Corporate and university bonds | 281,242 |  |  | 141 |  |  | (26,781) |  |  | 254,602 |
Total fixed maturity securities | 14,932,286 |  |  | 101,335 |  |  | (660,889) |  |  | 14,372,732 |
Short-term investments | 2,564,620 |  |  | 7,155 |  |  | (393) |  |  | 2,571,382 |
Investments, available-for-sale | $ | 17,496,906 |  |  | $ | 108,490 |  |  | $ | (661,282) |  |  | $ | 16,944,114 |
Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position | b) The following tables summarize gross unrealized investment losses on available-for-sale investments by the length of time that securities have continuously been in an unrealized loss position.
| December 31, 2024
| Less than 12 months |  | 12 months or longer |  | Total
(dollars in thousands) | Estimated Fair Value |  | Gross Unrealized Holding Losses |  | Estimated Fair Value |  | Gross Unrealized Holding Losses |  | Estimated Fair Value |  | Gross Unrealized Holding Losses
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury securities | $ | 1,593,711 |  |  | $ | (27,213) |  |  | $ | 1,444,869 |  |  | $ | (41,256) |  |  | $ | 3,038,580 |  |  | $ | (68,469) |
U.S. government-sponsored enterprises | 415,333 |  |  | (10,938) |  |  | 691,781 |  |  | (90,973) |  |  | 1,107,114 |  |  | (101,911) |
Obligations of states, municipalities and political subdivisions | 1,133,275 |  |  | (21,242) |  |  | 2,024,298 |  |  | (178,278) |  |  | 3,157,573 |  |  | (199,520) |
Foreign governments, agencies and supranationals | 1,056,877 |  |  | (29,890) |  |  | 1,246,215 |  |  | (177,412) |  |  | 2,303,092 |  |  | (207,302) |
Agency mortgage-backed securities | 757,562 |  |  | (13,880) |  |  | 1,710,436 |  |  | (109,992) |  |  | 2,467,998 |  |  | (123,872) |
Non-agency mortgage-backed securities | — |  |  | — |  |  | 118,030 |  |  | (4,343) |  |  | 118,030 |  |  | (4,343) |
Corporate and university bonds | 2,107 |  |  | (137) |  |  | 212,404 |  |  | (30,870) |  |  | 214,511 |  |  | (31,007) |
Total fixed maturity securities | 4,958,865 |  |  | (103,300) |  |  | 7,448,033 |  |  | (633,124) |  |  | 12,406,898 |  |  | (736,424) |
Short-term investments | 163,503 |  |  | (6,579) |  |  | — |  |  | — |  |  | 163,503 |  |  | (6,579) |
Total | $ | 5,122,368 |  |  | $ | (109,879) |  |  | $ | 7,448,033 |  |  | $ | (633,124) |  |  | $ | 12,570,401 |  |  | $ | (743,003) |
| December 31, 2023
| Less than 12 months |  | 12 months or longer |  | Total
(dollars in thousands) | Estimated Fair Value |  | Gross Unrealized Holding Losses |  | Estimated Fair Value |  | Gross Unrealized Holding Losses |  | Estimated Fair Value |  | Gross Unrealized Holding Losses
Fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury securities | $ | 317,027 |  |  | $ | (2,147) |  |  | $ | 1,507,784 |  |  | $ | (60,257) |  |  | $ | 1,824,811 |  |  | $ | (62,404) |
U.S. government-sponsored enterprises | 145,143 |  |  | (2,134) |  |  | 723,537 |  |  | (87,770) |  |  | 868,680 |  |  | (89,904) |
Obligations of states, municipalities and political subdivisions | 679,124 |  |  | (3,881) |  |  | 2,332,281 |  |  | (177,697) |  |  | 3,011,405 |  |  | (181,578) |
Foreign governments, agencies and supranationals | 83,396 |  |  | (394) |  |  | 1,492,912 |  |  | (141,614) |  |  | 1,576,308 |  |  | (142,008) |
Agency mortgage-backed securities | 189,977 |  |  | (1,872) |  |  | 1,889,272 |  |  | (133,739) |  |  | 2,079,249 |  |  | (135,611) |
Non-agency mortgage-backed securities | — |  |  | — |  |  | 333,070 |  |  | (22,603) |  |  | 333,070 |  |  | (22,603) |
Corporate and university bonds | — |  |  | — |  |  | 236,205 |  |  | (26,781) |  |  | 236,205 |  |  | (26,781) |
Total fixed maturity securities | 1,414,667 |  |  | (10,428) |  |  | 8,515,061 |  |  | (650,461) |  |  | 9,929,728 |  |  | (660,889) |
Short-term investments | 52,601 |  |  | (393) |  |  | — |  |  | — |  |  | 52,601 |  |  | (393) |
Total | $ | 1,467,268 |  |  | $ | (10,821) |  |  | $ | 8,515,061 |  |  | $ | (650,461) |  |  | $ | 9,982,329 |  |  | $ | (661,282) |
Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturities By Contractual Maturity | c) The amortized cost and estimated fair value of fixed maturity securities at December 31, 2024 are shown below by contractual maturity.
(dollars in thousands) | Amortized Cost |  | Estimated Fair Value
Due in one year or less | $ | 1,593,149 |  |  | $ | 1,571,022 |
Due after one year through five years | 6,071,013 |  |  | 5,901,682 |
Due after five years through ten years | 4,647,538 |  |  | 4,406,225 |
Due after ten years | 1,252,061 |  |  | 1,098,767 |
| 13,563,761 |  |  | 12,977,696 |
Mortgage-backed securities | 2,893,962 |  |  | 2,767,843 |
Total fixed maturity securities | $ | 16,457,723 |  |  | $ | 15,745,539 |
Components Of Net Investment Income | d) The following table presents the components of net investment income.
| Years Ended December 31,
(dollars in thousands) | 2024 |  | 2023 |  | 2022
Interest: |  |  |  |  |
Fixed maturity securities | $ | 510,044 |  |  | $ | 383,022 |  |  | $ | 294,417 |
Short-term investments | 124,575 |  |  | 106,747 |  |  | 33,493 |
Cash and cash equivalents and restricted cash and cash equivalents | 161,488 |  |  | 145,074 |  |  | 28,890 |
Dividends on equity securities | 142,367 |  |  | 116,911 |  |  | 107,213 |
| 938,474 |  |  | 751,754 |  |  | 464,013 |
Investment expenses | (17,978) |  |  | (17,222) |  |  | (17,258) |
Net investment income | $ | 920,496 |  |  | $ | 734,532 |  |  | $ | 446,755 |
Summary Of Net Realized Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments | e) The following table presents the components of net investment gains (losses) included in net income (loss) and the pre-tax change in net unrealized losses included in other comprehensive income (loss). Gross realized investment gains and losses on fixed maturity securities, short-term investments and other investments were not material to the consolidated financial statements and are presented on a net basis in the following table.
| Years Ended December 31,
(dollars in thousands) | 2024 |  | 2023 |  | 2022
Fixed maturity securities, short-term investments and other investments: |  |  |  |  |
Net realized investment gains (losses) | $ | 4,423 |  |  | $ | (42,177) |  |  | $ | (40,983) |
Equity securities: |  |  |  |  |
Change in fair value of securities sold during the period | (14,966) |  |  | 34,684 |  |  | (14,884) |
Change in fair value of securities held at the end of the period | 1,817,762 |  |  | 1,531,547 |  |  | (1,539,866) |
Total change in fair value | 1,802,796 |  |  | 1,566,231 |  |  | (1,554,750) |
Net investment gains (losses) | $ | 1,807,219 |  |  | $ | 1,524,054 |  |  | $ | (1,595,733) |
Change in net unrealized losses on available-for-sale investments included in other comprehensive income (loss): |  |  |  |  |
Fixed maturity securities | $ | (152,630) |  |  | $ | 389,498 |  |  | $ | (1,474,890) |
Short-term investments | (12,793) |  |  | 1,060 |  |  | 11,014 |
Net increase (decrease) | $ | (165,423) |  |  | $ | 390,558 |  |  | $ | (1,463,876) |
Schedule of Restricted Assets | f) Total restricted assets are included on the Company's consolidated balance sheets as follows.
| December 31,
(dollars in thousands) | 2024 |  | 2023
Fixed maturity securities | $ | 3,027,863 |  |  | $ | 3,102,899 |
Equity securities | 915,242 |  |  | 1,004,347 |
Short-term investments | 704,201 |  |  | 807,138 |
Restricted cash and cash equivalents | 499,581 |  |  | 584,974 |
Total | $ | 5,146,887 |  |  | $ | 5,499,358 |
Components Of Restricted Assets | The following table presents the components of restricted assets.
| December 31,
(dollars in thousands) | 2024 |  | 2023
Assets held in trust or on deposit to support underwriting activities | $ | 4,727,799 |  |  | $ | 5,048,857 |
Assets pledged as security for letters of credit | 419,088 |  |  | 450,501 |
Total | $ | 5,146,887 |  |  | $ | 5,499,358 |

X
- Definition [Table Text Block] for Components Of Restricted Assets [Table] + References No definition available. + Details
Name: | mkl_ComponentsOfRestrictedAssetsTableTextBlock
Namespace Prefix: | mkl_
Data Type: | dtr-types1:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition A tabular disclosure of restricted assets, by major category. + References No definition available. + Details
Name: | mkl_ScheduleOfRestrictedAssetsTableTextBlock
Namespace Prefix: | mkl_
Data Type: | dtr-types1:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of realized and unrealized gain (loss) on investment in security. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(c)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 + Details
Name: | us-gaap_GainLossOnInvestmentsTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of investment income, including, but not limited to, interest and dividend income and amortization of discount (premium) derived from debt and equity securities. Excludes realized and unrealized gain (loss) on investments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(8)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(a)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(b)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 + Details
Name: | us-gaap_InvestmentIncomeTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. + References No definition available. + Details
Name: | us-gaap_InvestmentsClassifiedByContractualMaturityDateTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value. + References No definition available. + Details
Name: | us-gaap_ScheduleOfAvailableForSaleSecuritiesReconciliationTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition For all investments in an unrealized loss position, including those for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), a tabular disclosure of the aggregate related fair value of investments with unrealized losses and the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value). + References Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-6 + Details
Name: | us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration