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Reserve for Losses and Loss Adjustment Expenses - Prior years reserve development (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | $ (600) | $ (507) | $ (538)
Operating segments |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (600) | (507) | (538)
Operating segments | Short-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (682) | (567) | (631)
Operating segments | Long-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | 82 | 60 | 93
Operating segments | Insurance |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (43) | (37) | (42)
Operating segments | Insurance | Short-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (61) | (53) | (85)
Operating segments | Insurance | Short-tailed lines | Travel and accident |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (26) | (32) | (15)
Operating segments | Insurance | Short-tailed lines | Property, energy, marine and aviation |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (21) |  | (43)
Operating segments | Insurance | Short-tailed lines | Surety |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse |  | (31) |
Operating segments | Insurance | Short-tailed lines | Warranty and lenders solutions |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse |  |  | (22)
Operating segments | Insurance | Long-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | 18 | 16 | 43
Operating segments | Insurance | Long-tailed lines | Professional liability |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse |  |  | 50
Operating segments | Reinsurance |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (322) | (188) | (152)
Operating segments | Reinsurance | Short-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (386) | (232) | (202)
Operating segments | Reinsurance | Short-tailed lines | Property excluding property catastrophe |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (178) | (99) | (93)
Operating segments | Reinsurance | Short-tailed lines | Other specialty lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse |  | (74) | (35)
Operating segments | Reinsurance | Short-tailed lines | Property catastrophe |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (141) | (64) | (51)
Operating segments | Reinsurance | Long-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | 64 | 44 | 50
Operating segments | Reinsurance | Long-tailed lines | Casualty |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | 64 | 44 | 45
Operating segments | Mortgage |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (235) | (282) | (344)
Operating segments | Mortgage | Short-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (235) | (282) | (344)
Operating segments | Mortgage | Long-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | $ 0 | $ 0 | $ 0

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