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Unpaid losses and loss expenses (RF) (Details) - USD ($) $ in Millions | 6 Months Ended
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Jun. 30, 2025 | Jun. 30, 2024
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |
Gross unpaid losses and loss expenses – beginning of period |  | $ 84,004 | $ 80,122
Reinsurance recoverable on unpaid losses and loss expenses - beginning of period | [1] | 17,734 | 17,884
Net unpaid losses and loss expenses – beginning of period |  | 66,270 | 62,238
Current Year Claims and Claims Adjustment Expense |  | 13,959 | 12,604
Prior Year Claims and Claims Adjustment Expense | [2] | (491) | (446)
Total, Incurred |  | 13,468 | 12,158
Net loss and loss expenses paid, Current Year |  | 2,960 | 2,492
Net loss and loss expenses paid, Prior Years |  | 8,982 | 6,918
Total, Paid |  | 11,942 | 9,410
Foreign currency revaluation and other |  | 889 | (204)
Net unpaid losses and loss expenses – end of period |  | 68,685 | 64,782
Reinsurance recoverable on unpaid losses and loss expenses - end of period | [1] | (17,691) | (17,409)
Gross unpaid losses and loss expenses – end of period |  | 86,376 | 82,191
prior period development, net adjustments |  | $ (13) | $ 47
[1] | Net of valuation allowance for uncollectible reinsurance.
[2] | Relates to prior period loss reserve development only and excludes prior period development related to reinstatement premiums, expense adjustments, earned premiums, and A&H long-duration lines totaling $(13) million and $47 million for the six months ended June 30, 2025 and 2024, respectively.

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- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 55 -Paragraph 11 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477548/944-605-55-11 Reference 2: 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 3: http://www.xbrl.org/2003/role/exampleRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 55 -Paragraph 9E -Publisher FASB -URI https://asc.fasb.org/1943274/2147480046/944-40-55-9E Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (cc) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-3 Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(13)(a)(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478777/944-210-S99-1 + Details
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- Definition Amount, after effects of reinsurance, of payments to settle claims incurred in the current period 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 (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-3 + Details
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- Definition Amount of foreign currency gain (loss) which decreases (increases) the cost of settling unpaid claims after deduction of reinsurance recoveries. Includes, but is not limited to, claims which have been incurred but not reported. + References No definition available. + Details
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