XML 72 R47.htm IDEA: XBRL DOCUMENT
v3.25.4

Municipal Bond Guarantee Reinsurance (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2025
Guarantees [Abstract] |
Schedule of nominal and fair value of notes receivable | The following table presents the changes in the nominal value and fair value of the BAM Surplus Notes for the year ended December 31, 2025:
Millions |  | Year Ended December 31, 2025 |  |  |
Beginning nominal value |  | $ | 495.7 |  |  |  |
Interest income from BAM Surplus Notes |  | 29.8 |  |  |  |
Payments of principal and interest |  | (35.0) |  |  |  |
Ending nominal value |  | 490.5 |  |  |  |
Beginning fair value discount |  | (114.0) |  |  |  |
Change in fair value of BAM Surplus Notes |  | (37.5) |  |  |  |
Ending fair value discount |  | (151.5) |  |  |  |
BAM Surplus Notes, at fair value |  | $ | 339.0 |  |  |  |
Schedule of insured obligations | The following table presents the HG Global segment’s insured obligations as of December 31, 2025 and 2024:
|  | December 31, 2025 |  | December 31, 2024 |
Contracts outstanding |  | 17,377 |  |  | 15,884 |  |
Remaining weighted average contract period (in years) (1) |  | 11.6 |  | 11.2 |
Outstanding par value of policies assumed (in millions) (2) |  | $ | 20,559.9 |  |  | $ | 18,503.3 |  |
Gross unearned insurance premiums (in millions) |  | $ | 327.9 |  |  | $ | 297.3 |  |
(1) The remaining weighted average contract period was calculated using total contractual debt service outstanding, including principal and interest. (2) Under the FLRT, HG Re provides first-loss reinsurance protection of up to 15%-of-par outstanding for each policy assumed from BAM. For capital appreciation bonds, par is adjusted to the estimated equivalent par value for current interest paying bonds.
Schedule of HG's future premium revenues | The following table presents the HG Global segment’s future premium revenues as of December 31, 2025:
Millions |  | December 31, 2025
January 1, 2026 - March 31, 2026 |  | $ | 7.1 |
April 1, 2026 - June 30, 2026 |  | 7.0 |
July 1, 2026 - September 30, 2026 |  | 6.9 |
October 1, 2026 - December 31, 2026 |  | 6.8 |
Total 2026 |  | 27.8 |
2027 |  | 26.4 |
2028 |  | 24.8 |
2029 |  | 23.3 |
2030 |  | 21.9 |
2031 and thereafter |  | 203.7 |
Total gross unearned insurance premiums |  | $ | 327.9 |
Effects of reinsurance | The following table summarizes the effects of reinsurance on written and earned premiums and on loss and LAE for the Ark/WM Outrigger segment for the years ended December 31, 2025, 2024 and 2023.
|  | Year Ended December 31,
Millions |  | 2025 |  | 2024 |  | 2023
Written premiums: |  |  |  |  |  |
Direct |  | $ | 1,260.1 |  |  | $ | 1,101.5 |  |  | $ | 931.9 |
Assumed |  | 1,297.1 |  |  | 1,105.5 |  |  | 966.5 |
Gross written premiums |  | 2,557.2 |  |  | 2,207.0 |  |  | 1,898.4 |
Ceded (1) |  | (745.6) |  |  | (527.9) |  |  | (377.5) |
Net written premiums |  | $ | 1,811.6 |  |  | $ | 1,679.1 |  |  | $ | 1,520.9 |
Earned premiums: |  |  |  |  |  |
Direct |  | $ | 1,130.9 |  |  | $ | 1,004.2 |  |  | $ | 848.1 |
Assumed |  | 1,198.9 |  |  | 1,088.2 |  |  | 925.6 |
Gross earned premiums |  | 2,329.8 |  |  | 2,092.4 |  |  | 1,773.7 |
Ceded (2) |  | (632.4) |  |  | (504.6) |  |  | (364.0) |
Net earned premiums |  | $ | 1,697.4 |  |  | $ | 1,587.8 |  |  | $ | 1,409.7 |
Loss and LAE: |  |  |  |  |  |
Gross |  | $ | 1,118.6 |  |  | $ | 1,056.7 |  |  | $ | 782.5 |
Ceded (3) |  | (274.4) |  |  | (200.9) |  |  | (55.7) |
Net loss and LAE |  | $ | 844.2 |  |  | $ | 855.8 |  |  | $ | 726.8 |
(1) The years ended December 31, 2025, 2024 and 2023 exclude written premiums of $84.2, $86.5 and $110.0 ceded by Ark to WM Outrigger Re, which eliminate in White Mountains’s consolidated financial statements. (2) The years ended December 31, 2025, 2024 and 2023 exclude earned premiums of $84.6, $88.0 and $104.3 ceded by Ark to WM Outrigger Re, which eliminate in White Mountains’s consolidated financial statements. (3) The years ended December 31, 2025, 2024 and 2023 exclude loss and LAE of $25.4 and $29.9 and $15.6 ceded by Ark to WM Outrigger Re, which eliminate in White Mountains’s consolidated financial statements. The following table presents the Ark/WM Outrigger segment’s reinsurance recoverables as of December 31, 2025 and December 31, 2024:
Millions |  | December 31, 2025 |  | December 31, 2024
Reinsurance recoverables on unpaid losses (1) |  | $ | 508.3 |  |  | $ | 434.4 |
Reinsurance recoverables on paid losses (2) |  | 117.6 |  |  | 57.5 |
Ceded unearned premiums (3) |  | 210.2 |  |  | 97.1 |
Reinsurance recoverables |  | $ | 836.1 |  |  | $ | 589.0 |
(1) The reinsurance recoverables on unpaid losses exclude $29.5 and $31.8 ceded by Ark to WM Outrigger Re as of December 31, 2025 and 2024, which eliminate in White Mountains’s consolidated financial statements. (2) The reinsurance recoverables on paid losses exclude $5.2 and $3.1 ceded by Ark to WM Outrigger Re as of December 31, 2025 and 2024, which eliminates in White Mountains’s consolidated financial statements. (3) The ceded unearned premiums exclude $3.9 and $4.3 ceded by Ark to WM Outrigger Re as of December 31, 2025 and 2024, which eliminate in White Mountains’s consolidated financial statements. The following tables present gross written premiums and gross earned premiums included in the HG Global segment for the years ended December 31, 2025, 2024 and 2023:
|  | Year Ended December 31, 2025 |  |  |  |  |  |
Millions |  | HG Global |  |  |  |  |  |
Written premiums: |  |  |  |  |  |  |  |
Direct |  | $ | — |  |  |  |  |  |  |
Assumed |  | 61.4 |  |  |  |  |  |  |
Gross written premiums |  | $ | 61.4 |  |  |  |  |  |  |
Earned premiums: |  |  |  |  |  |  |  |
Direct |  | $ | — |  |  |  |  |  |  |
Assumed |  | 30.8 |  |  |  |  |  |  |
Gross earned premiums |  | $ | 30.8 |  |  |  |  |  |  |
|  | Year Ended December 31, 2024
Millions |  | HG Global |  | BAM |  | Eliminations |  | Total
Written premiums: |  |  |  |  |  |  |  |
Direct |  | $ | — |  |  | $ | 24.1 |  |  | $ | — |  |  | $ | 24.1 |
Assumed |  | 52.4 |  |  | — |  |  | (20.5) |  |  | 31.9 |
Gross written premiums (1) |  | $ | 52.4 |  |  | $ | 24.1 |  |  | $ | (20.5) |  |  | $ | 56.0 |
Earned premiums: |  |  |  |  |  |  |  |
Direct |  | $ | — |  |  | $ | 15.8 |  |  | $ | — |  |  | $ | 15.8 |
Assumed |  | 28.9 |  |  | 1.0 |  |  | (14.0) |  |  | 15.9 |
Gross earned premiums (1) |  | $ | 28.9 |  |  | $ | 16.8 |  |  | $ | (14.0) |  |  | $ | 31.7 |
(1) For the six months ended June 30, 2024, BAM ceded written premiums of $20.5 and earned premiums of $14.0 to HG Global, which eliminated in consolidation. Subsequent to the deconsolidation of BAM, there are no ceded premiums, such that gross written premiums and gross earned premiums are equivalent to net written premiums and net earned premiums, respectively.
|  | Year Ended December 31, 2023
Millions |  | HG Global |  | BAM |  | Eliminations |  | Total
Written premiums: |  |  |  |  |  |  |  |
Direct |  | $ | — |  |  | $ | 58.6 |  |  | $ | — |  |  | $ | 58.6 |
Assumed |  | 50.1 |  |  | — |  |  | (50.1) |  |  | — |
Gross written premiums (1) |  | $ | 50.1 |  |  | $ | 58.6 |  |  | $ | (50.1) |  |  | $ | 58.6 |
Earned premiums: |  |  |  |  |  |  |  |
Direct |  | $ | — |  |  | $ | 28.7 |  |  | $ | — |  |  | $ | 28.7 |
Assumed |  | 26.0 |  |  | 2.5 |  |  | (26.0) |  |  | 2.5 |
Gross earned premiums (1) |  | $ | 26.0 |  |  | $ | 31.2 |  |  | $ | (26.0) |  |  | $ | 31.2 |
(1) For the year ended December 31, 2023, BAM ceded written premiums of $50.1 and ceded earned premiums of $26.0 to HG Global, which eliminated in consolidation.

X
- Definition Tabular disclosure of the effects of reinsurance, for example, but not limited to, disclosure of direct, assumed, and ceded insurance. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479838/944-20-50-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
Name: | us-gaap_EffectsOfReinsuranceTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of financial guarantee insurance contracts in which premiums are received over the contract period. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477363/944-310-50-3 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 310 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477363/944-310-50-3 + Details
Name: | us-gaap_FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

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

X
- Definition [Table Text Block] for Schedule of Municipal Guarantee Insured Obligations [Table] + References No definition available. + Details
Name: | wtm_ScheduleOfMunicipalGuaranteeInsuredObligationsTableTextBlock
Namespace Prefix: | wtm_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Schedule of Nominal and Fair Value of Notes Receivable + References No definition available. + Details
Name: | wtm_ScheduleOfNominalAndFairValueOfNotesReceivableTableTextBlock
Namespace Prefix: | wtm_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration