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Business Segments (Segment Expenses Included Within Incurred Claims and Benefits) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Segment Reporting, Revenue Reconciling Item [Line Items] |  |  |
Net incurred claim and claim adjustment expenses related to current year | $ 1,093 | $ 922 | $ 821
(Favorable) unfavorable development | 48 | 48 | (32)
Property and Casualty Segments | Specialty |  |  |
Segment Reporting, Revenue Reconciling Item [Line Items] |  |  |
Net incurred claim and claim adjustment expenses related to current year | 2,010 | 1,937 | 1,877
Catastrophe losses | 0 | 0 | 2
(Favorable) unfavorable development | (9) | (14) | (40)
Property and Casualty Segments | Commercial |  |  |
Segment Reporting, Revenue Reconciling Item [Line Items] |  |  |
Net incurred claim and claim adjustment expenses related to current year | 3,217 | 2,801 | 2,419
Catastrophe losses | 318 | 207 | 222
(Favorable) unfavorable development | (16) | (22) | (43)
Property and Casualty Segments | International |  |  |
Segment Reporting, Revenue Reconciling Item [Line Items] |  |  |
Net incurred claim and claim adjustment expenses related to current year | 730 | 680 | 627
Catastrophe losses | 40 | 29 | 23
(Favorable) unfavorable development | $ (6) | $ 13 | $ (13)

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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 The charge against earnings in the period for the uninsured portion of a loss from a fire, explosion, or natural disaster (hurricane, earthquake). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 220 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2 + Details
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