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v3.25.4

Segment Information - Summary of net premiums written and earned by major line of business and net premiums written by location (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | $ 17,065 | $ 15,100 | $ 12,440
Net premiums written | 16,476 | 15,732 | 13,468
Operating segments | Insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 7,771 | 6,627 | 5,446
Net premiums written | 7,798 | 6,874 | 5,862
Operating segments | Insurance | North America |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 5,735 | 4,702 | 3,781
Net premiums written | 5,724 | 4,869 | 3,995
Operating segments | Insurance | International |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 2,036 | 1,925 | 1,665
Net premiums written | 2,074 | 2,005 | 1,867
Operating segments | Insurance | Property and short-tail specialty | North America |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 1,373 | 1,165 | 976
Operating segments | Insurance | Property and short-tail specialty | International |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 1,099 | 1,061 | 885
Operating segments | Insurance | Casualty and other | International |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 937 | 864 | 780
Operating segments | Insurance | Other liability - occurrence | North America |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 1,321 | 942 | 618
Operating segments | Insurance | Other liability - claims made | North America |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 786 | 843 | 866
Operating segments | Insurance | Commercial multi-peril | North America |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 792 | 435 | 193
Operating segments | Insurance | Commercial automobile | North America |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 581 | 459 | 343
Operating segments | Insurance | Workers compensation | North America |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 591 | 549 | 495
Operating segments | Insurance | Other | North America |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 291 | 309 | 290
Operating segments | Reinsurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 8,122 | 7,242 | 5,836
Net premiums written | 7,618 | 7,746 | 6,554
Operating segments | Reinsurance | Bermuda |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums written | 3,672 | 3,425 | 3,288
Operating segments | Reinsurance | United States |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums written | 1,798 | 2,135 | 1,756
Operating segments | Reinsurance | Europe and other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums written | 2,148 | 2,186 | 1,510
Operating segments | Reinsurance | Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 150 | 152 | 118
Operating segments | Reinsurance | Specialty |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 2,906 | 2,619 | 2,097
Operating segments | Reinsurance | Property excluding property catastrophe |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 2,252 | 2,148 | 1,645
Operating segments | Reinsurance | Casualty |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 1,432 | 1,088 | 1,005
Operating segments | Reinsurance | Property catastrophe |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 1,065 | 959 | 742
Operating segments | Reinsurance | Marine and aviation |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 317 | 276 | 229
Operating segments | Mortgage |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 1,172 | 1,231 | 1,158
Net premiums written | 1,060 | 1,112 | 1,052
Operating segments | Mortgage | United States |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums written | 780 | 823 | 743
Operating segments | Mortgage | Other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums written | 280 | 289 | 309
Operating segments | Mortgage | U.S. primary mortgage insurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 802 | 845 | 759
Operating segments | Mortgage | U.S. credit risk transfer (CRT) and other |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | 207 | 213 | 220
Operating segments | Mortgage | International mortgage insurance/reinsurance |  |  |
Segment Reporting Information [Line Items] |  |  |
Net premiums earned | $ 163 | $ 173 | $ 179

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