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Reserve for Property and Casualty Insurance Claims and Claims Expense - Incurred and claims expense (Details) $ in Millions |  |  | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 14, 2020 USD ($) | Jul. 01, 2020 USD ($) | Mar. 31, 2021 USD ($) | Sep. 30, 2020 USD ($) settlement | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Jan. 22, 2021 USD ($) | Jun. 20, 2020 USD ($)
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | $ (436) | $ (130) | $ (255) |  |
Reinsurance expected recovery percentage |  | 80.00% |  |  |  |  |  |  |
Auto |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (107) | (323) | (455) |  |
Homeowners |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (439) | 65 | 14 |  |
Other personal lines |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (66) | 8 | (7) |  |
Commercial lines |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | 36 | 17 | 108 |  |
Discontinued Lines and Coverages |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | 141 | 105 | 87 |  |
Protection Services |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (1) | (2) | (2) |  |
Catastrophe losses |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  | $ (495) | (503) | 48 | 25 |  |
Number of settlements | settlement |  |  |  | 2 |  |  |  |  |
Catastrophe losses | Auto |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (44) | (17) | (39) |  |
Catastrophe losses | Homeowners |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (422) | 66 | 65 |  |
Catastrophe losses | Other personal lines |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (39) | 0 | (1) |  |
Catastrophe losses | Commercial lines |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | 2 | (1) | 0 |  |
Catastrophe losses | Discontinued Lines and Coverages |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | 0 | 0 | 0 |  |
Catastrophe losses | Protection Services |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | 0 | 0 | 0 |  |
Fire | Pacific Gas And Electric |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  | $ (450) |  |  |  |  |  |  |
Catastrophe reinsurance settlement amount |  |  |  |  |  |  |  |  | $ 11,000
Fire | Southern California Edison |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years | $ (45) |  |  |  |  |  |  |  |
Catastrophe reinsurance settlement amount | $ 1,160 |  |  |  |  |  |  |  |
Fire | Southern California Edison | Forecast |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  | $ (110) |  |  |  |  |  |
Fire | Southern California Edison | Subsequent Event |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Catastrophe reinsurance settlement amount |  |  |  |  |  |  |  | $ 2,200 |
Non-catastrophe losses |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | 67 | (178) | (280) |  |
Non-catastrophe losses | Auto |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (63) | (306) | (416) |  |
Non-catastrophe losses | Homeowners |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (17) | (1) | (51) |  |
Non-catastrophe losses | Other personal lines |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (27) | 8 | (6) |  |
Non-catastrophe losses | Commercial lines |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | 34 | 18 | 108 |  |
Non-catastrophe losses | Discontinued Lines and Coverages |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | 141 | 105 | 87 |  |
Non-catastrophe losses | Protection Services |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | (1) | $ (2) | $ (2) |  |
Annual reserve review | Discontinued Lines and Coverages |  |  |  |  |  |  |  |  |
Increase (decrease) in claims and claims expense |  |  |  |  |  |  |  |  |
Prior years |  |  |  |  | $ 132 |  |  |  |

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