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Reserve for Losses and Loss Adjustment Expenses - Prior year development (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development favorable (unfavorable) | $ 124 | $ 136
Operating segments | Insurance |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development favorable (unfavorable) | $ 10 | $ 12
Percentage of prior year development | 0.70% | 0.90%
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) | $ (20) | $ (13)
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) |  | (18)
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) | (17) | 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) | 7 | 1
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) | 3 |
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) | (7) |
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) | 18 | 9
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) |  | 7
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) | 10 | 8
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) | 30 | 25
Operating segments | Reinsurance |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development favorable (unfavorable) | $ 40 | $ 53
Percentage of prior year development | 2.40% | 4.00%
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) | $ (2) | $ 2
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) | (2) | 3
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) | 44 | 49
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) | (8) | 8
Operating segments | Reinsurance | Short tailed lines | Property other than property catastrophe |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development favorable (unfavorable) | 21 | 23
Operating segments | Reinsurance | Short tailed lines | Other specialty lines and other lines |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development favorable (unfavorable) |  | 18
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) | 33 |
Operating segments | Reinsurance | 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) | (4) | 3
Operating segments | Mortgage |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |
Prior year development favorable (unfavorable) | $ 74 | $ 71
Percentage of prior year development | 24.40% | 23.90%

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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/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 7 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-7 Reference 2: 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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