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Unpaid losses and loss adjustment expenses - Narrative (Detail) - Property and Casualty Insurance and Reinsurance, Excluding Retroactive Reinsurance [Member] - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2024 | Mar. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Incurred losses and loss adjustment expenses, prior accident years | $ (634) | $ (740)
Prior years' losses incurred as a percentage of net liabilities | 0.60% | 0.70%
Primary Insurance Businesses [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Incurred losses and loss adjustment expenses, prior accident years | $ (248) | $ (379)
Property and Casualty Reinsurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Incurred losses and loss adjustment expenses, prior accident years | $ (386) | $ (361)

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- Definition Prior year claims and claims adjustment expense as a percentage of the beginning of period net liability for unpaid claims and claims adjustment expenses. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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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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