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Reserve for Property and Casualty Insurance Claims and Claims Expense - Prior year reserve reestimates included in claims and claims expense (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Increase (decrease) in claims and claims expense |  |
Prior years | $ (241) | $ 8
Auto |  |
Increase (decrease) in claims and claims expense |  |
Prior years | (36) | 13
Homeowners |  |
Increase (decrease) in claims and claims expense |  |
Prior years | (203) | (7)
Other personal lines |  |
Increase (decrease) in claims and claims expense |  |
Prior years | (18) | (6)
Commercial lines |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 15 | 6
Run-off Property-Liability |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 1 | 2
Non-catastrophe losses |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 2 | 28
Non-catastrophe losses | Auto |  |
Increase (decrease) in claims and claims expense |  |
Prior years | (17) | 22
Non-catastrophe losses | Homeowners |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 5 | 1
Non-catastrophe losses | Other personal lines |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 0 | (2)
Non-catastrophe losses | Commercial lines |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 13 | 5
Non-catastrophe losses | Run-off Property-Liability |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 1 | 2
Catastrophe |  |
Increase (decrease) in claims and claims expense |  |
Prior years | (243) | (20)
Catastrophe | Nationwide Aggregate Reinsurance Program |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 150 |
Catastrophe | Auto |  |
Increase (decrease) in claims and claims expense |  |
Prior years | (19) | (9)
Catastrophe | Homeowners |  |
Increase (decrease) in claims and claims expense |  |
Prior years | (208) | (8)
Catastrophe | Other personal lines |  |
Increase (decrease) in claims and claims expense |  |
Prior years | (18) | (4)
Catastrophe | Commercial lines |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 2 | 1
Catastrophe | Run-off Property-Liability |  |
Increase (decrease) in claims and claims expense |  |
Prior years | 0 | $ 0
Fire | Southern California Edison |  |
Increase (decrease) in claims and claims expense |  |
Prior years | $ 110 |

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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 -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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