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Third-Party Reinsurance (Tables) | 12 Months Ended
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Dec. 31, 2025
Reinsurance Disclosures [Abstract] |
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.
Gross and net reinsurance recoverables by reinsurers ratings | The following table presents the Ark/WM Outrigger segment’s gross and net reinsurance recoverables by the reinsurers’ A.M. Best Company, Inc (“A.M. Best”) ratings as of December 31, 2025:
$ in Millions |  | As of December 31, 2025
A.M. Best Rating (1) |  | Gross |  | Collateral |  | Net |  | % of Total
A+ or better |  | $ | 404.0 |  |  | $ | — |  |  | $ | 404.0 |  |  | 71.7 | %
A- to A |  | 147.7 |  | — |  |  | 147.7 |  | 26.2 |
B++ or lower and not rated |  | 74.2 | (2) | 62.3 | (2) | 11.9 |  | 2.1 |
Total |  | $ | 625.9 |  |  | $ | 62.3 |  |  | $ | 563.6 |  |  | 100.0 | %
(1) A.M. Best financial strength ratings as detailed above are: “A+ or better” (Superior) “A- to A” (Excellent), “B++” (Good). (2) Excludes $34.7 ceded by Ark to WM Outrigger Re as of December 31, 2025, which eliminates in White Mountains’s consolidated financial statements.

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- 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
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- Definition Tabular disclosure of reinsurer or group of reinsurers for whom the entity has a concentration of credit risk. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name Accounting Standards Codification -Section 50 -Paragraph 1B -SubTopic 825 -Topic 944 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477351/944-825-50-1B + Details
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