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Reserve for Property and Casualty Insurance Claims and Claims Expense - Schedule of Prior Year Reserve Re-Estimates Included in Claims and Claims Expense (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | $ (424) | $ 32 | $ (1,045) | $ (322)
Auto |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (483) | (65) | (1,163) | (319)
Homeowners |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (54) | (12) | (32) | (392)
Other personal lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 66 | 51 | 142 | 164
Commercial lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (85) | 1 | (104) | 159
Other business lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (14) | (3) | (39) | 1
Run-off Property-Liability |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 146 | 59 | 151 | 65
Protection Services |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 0 | 1 | 0 | 0
Catastrophe losses |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (28) | (14) | (38) | (314)
Catastrophe losses | Auto |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (3) | (10) | (30) | (26)
Catastrophe losses | Homeowners |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (14) | (1) | 3 | (278)
Catastrophe losses | Other personal lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (6) | (3) | (11) | (5)
Catastrophe losses | Commercial lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (5) | 0 | 0 | (5)
Catastrophe losses | Other business lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 0 | 0 | 0 | 0
Catastrophe losses | Run-off Property-Liability |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 0 | 0 | 0 | 0
Catastrophe losses | Protection Services |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 0 | 0 | 0 | 0
Nationwide Reinsurance Program |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years |  |  | 69 |
2021 Colorado Marshall Fire |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years |  |  | 54 |
Non-catastrophe losses |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (396) | 46 | (1,007) | (8)
Non-catastrophe losses | Auto |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (480) | (55) | (1,133) | (293)
Non-catastrophe losses | Homeowners |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (40) | (11) | (35) | (114)
Non-catastrophe losses | Other personal lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 72 | 54 | 153 | 169
Non-catastrophe losses | Commercial lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (80) | 1 | (104) | 164
Non-catastrophe losses | Other business lines |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | (14) | (3) | (39) | 1
Non-catastrophe losses | Run-off Property-Liability |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 146 | 59 | 151 | 65
Non-catastrophe losses | Protection Services |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 0 | $ 1 | 0 | 0
Favorable Severity Development | Personal auto injury coverage |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | 284 |  | 565 |
Favorable Severity Development | Personal auto physical damage coverage |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years | $ 196 |  | 568 |
Annual Reserve Review | Run-off Property-Liability |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |
Prior years |  |  | $ 146 | $ 58

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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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