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Short Duration Contracts - Reconciliation of claims development to liability (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
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Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | $ 23,906 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 9,054 | $ 7,821 | $ 6,690 | $ 6,280
Lines other than short duration |  | 136 |  |  |
Discounting |  | (78) |  |  |
Unallocated claims adjustment expenses |  | 529 |  |  |
Total reconciling items |  | 587 |  |  |
Reserve for losses and loss adjustment expenses |  | 33,547 | $ 29,369 | $ 22,752 | $ 20,032
Other short duration lines not included |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance | [1] | 1,436 |  |  |
Unpaid losses and loss adjustment expenses recoverable | [2] | 271 |  |  |
Other short duration lines not included | Loss portfolio transfer |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Unpaid losses and loss adjustment expenses recoverable | [2] | 121 |  |  |
Total for short duration lines |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 9,054 |  |  |
Insurance | Property, energy, marine and aviation |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 975 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 456 |  |  |
Insurance | Third party occurrence business |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 4,454 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 2,893 |  |  |
Insurance | Third party claims-made business |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 2,814 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 907 |  |  |
Insurance | Multi-line and other specialty |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 2,827 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 436 |  |  |
Reinsurance | Casualty |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 3,785 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 861 |  |  |
Reinsurance | Property catastrophe |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 920 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 911 |  |  |
Reinsurance | Property excluding property catastrophe |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 2,103 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 362 |  |  |
Reinsurance | Marine and aviation |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 612 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 549 |  |  |
Reinsurance | Specialty |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 3,669 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 1,386 |  |  |
Mortgage |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Liabilities for losses and loss adjustment expenses, net of reinsurance |  | 311 |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | 42 |  |  |
Consolidating adjustments and eliminations |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |
Unpaid losses and loss adjustment expenses recoverable |  | $ (20) |  |  |
[1] | Includes amounts primarily associated with the loss portfolio reinsurance agreement related to the MCE Acquisition.
[2] | Includes unpaid loss and loss adjustment expenses recoverable of $121 million related to the loss portfolio transfer reinsurance agreements.

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