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Reserve for Losses and Loss Adjustment Expenses - Prior years reserve development (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | $ (507) | $ (538) | $ (769)
Operating segments |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (507) | (538) | (769)
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 | (567) | (631) | (814)
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 | 60 | 93 | 45
Operating segments | Insurance |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (37) | (42) | (25)
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 | (53) | (85) | (65)
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 | (32) | (15) | (15)
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 | Property and marine |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse |  | (43) |
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) | (37)
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 | 16 | 43 | 40
Operating segments | Insurance | 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 |  |  | 18
Operating segments | Insurance | Long-tailed lines | Professional Liability Insurance |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse |  | 50 | 25
Operating segments | Reinsurance |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (188) | (152) | (190)
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 | (232) | (202) | (195)
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 | (99) | (93) | (109)
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) | (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 | (64) | (51) | (24)
Operating segments | Reinsurance | Short-tailed lines | Marine and aviation |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse |  |  | (28)
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 | 44 | 50 | 5
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 | 44 | 45 | 5
Operating segments | Mortgage |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year reserve development (favorable) adverse | (282) | (344) | (554)
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 | (282) | (344) | (554)
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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