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Reserve for Losses and Loss Adjustment Expenses - Prior years reserve development (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | $ 538 | $ 769 | $ 355
Operating segments | Insurance |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | $ 42 | $ 25 | $ 16
Prior year reserve development (points) | 0.80% | 0.60% | 0.40%
Operating segments | Insurance | Short-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) |  | $ 55 | $ 82
Operating segments | Insurance | Short-tailed lines | Property Excluding Marine |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | $ 32 |  | 39
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 development favorable (unfavorable) | 15 | 15 | 16
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 development favorable (unfavorable) | 22 | 37 | 27
Operating segments | Insurance | Medium-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | (65) |  | (94)
Operating segments | Insurance | Medium-tailed lines | Professional liability |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | (50) | (25) | (31)
Operating segments | Insurance | Medium-tailed lines | Contract binding |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | (21) | (6) | (58)
Operating segments | Insurance | Medium-tailed lines | Marine |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | 12 | 13 |
Operating segments | Insurance | Long-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) |  |  | 28
Operating segments | Insurance | Long-tailed lines | Casualty |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) |  | (19) |
Operating segments | Insurance | Long-tailed lines | Other business |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) |  | 22 |
Operating segments | Insurance | Long-tailed lines | Construction and national accounts |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | (6) | (7) |
Operating segments | Insurance | Long-tailed lines | Executive assurance |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | 28 |  |
Operating segments | Insurance | Long-tailed lines | Alternative Markets |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | 17 |  |
Operating segments | Insurance | Medium-tailed and long-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) |  | (30) |
Operating segments | Insurance | Short Tailed And Long Tailed Lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | 107 |  | 110
Operating segments | Reinsurance |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | $ 152 | $ 190 | $ 179
Prior year reserve development (points) | 2.60% | 4.80% | 6.30%
Operating segments | Reinsurance | Short-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) |  |  | $ 176
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 development favorable (unfavorable) | $ 51 | $ 24 | (36)
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 development favorable (unfavorable) | 93 | 109 | 89
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 development favorable (unfavorable) | 35 | 35 | 123
Operating segments | Reinsurance | Short-tailed lines | Other business |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | 13 |  |
Operating segments | Reinsurance | Medium-tailed lines | Marine and aviation |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | 9 | 28 |
Operating segments | Reinsurance | Long-tailed lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | (50) | (5) | (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 development favorable (unfavorable) | (46) | (5) |
Operating segments | Reinsurance | Short Tailed And Medium Tailed Lines |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | 202 | 196 | 184
Operating segments | Mortgage |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) | $ 344 | $ 554 | $ 170
Prior year reserve development (points) | 29.70% | 47.80% | 13.20%
Operating segments | Other |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |
Prior year development favorable (unfavorable) |  |  | $ (8)

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- Definition Amount, after effects of reinsurance, of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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