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Insurance Claim Reserves (Details) - Prior Year Reserve Development - Property-casualty [Member] - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Liability for claims and claim adjustment expense |  |  |  |
Net favorable development included in estimated claims and claim adjustment expenses incurred for claims arising in prior years |  |  | $ 648 | $ 321
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations |  |  | 715 | 447
Accretion expense |  |  | 32 | 33
Business Insurance [Member] |  |  |  |
Liability for claims and claim adjustment expense |  |  |  |
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations | $ (125) | $ (91) | 28 | (57)
Business Insurance [Member] | Asbestos reserves [Member] |  |  |  |
Liability for claims and claim adjustment expense |  |  |  |
Increase to reserves | 277 | 242 | 277 | 242
Bond & Specialty Insurance [Member] |  |  |  |
Liability for claims and claim adjustment expense |  |  |  |
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations | 43 | 36 | 191 | 84
Personal Insurance [Member] |  |  |  |
Liability for claims and claim adjustment expense |  |  |  |
Net favorable (unfavorable) prior year reserve development impacting the Company's results of operations | $ 104 | $ 181 | $ 496 | $ 420

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- Definition Amount of benefit (expense) for claims incurred in prior reporting periods and related claims settlement costs impacting the Company's results of operations. + References No definition available. + Details
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- Definition Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 35 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481639/420-10-35-4 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 420 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482017/420-10-50-1 + Details
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- Definition The increase (decrease) during the reporting period in asbestos and environmental claims reserve, net of reinsurance recoveries. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480081/944-40-50-3 + 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/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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