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Claim and Claim Adjustment Expense Reserves (Commercial - General Liability - Net Strengthening or Releasing of Prior Accident Year Reserves) (Details) - Commercial - USD ($) $ in Millions | 12 Months Ended | 24 Months Ended | 36 Months Ended | 48 Months Ended | 60 Months Ended | 72 Months Ended | 84 Months Ended | 96 Months Ended | 108 Months Ended | 120 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2023 | Dec. 31, 2023
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | $ 75 | $ 149 | $ 67 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 65 | 148 | 57 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total net development for accident years prior to 2015 | 10 | 1 | 10 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total unallocated claim adjustment expense development | 0 | 0 | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total | 75 | 149 | 67 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General Liability | 2015 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 17 | 14 | 8 | $ 15 | $ 2 | $ 11 | $ 15 | $ (2) | $ (5) |  |  |  |  |  |  |  |  | $ 75
General Liability | 2016 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 8 | 20 | 1 | 10 | 2 | 4 | 8 | $ 36 |  |  |  |  |  |  |  |  | $ 89 |
General Liability | 2017 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 23 | 38 | 22 | (4) | 2 | 0 | $ 0 |  |  |  |  |  |  |  |  | $ 81 |  |
General Liability | 2018 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (14) | 29 | 11 | (7) | 2 | $ (9) |  |  |  |  |  |  |  |  | $ 12 |  |  |
General Liability | 2019 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 7 | 29 | 9 | 0 | $ 2 |  |  |  |  |  |  |  |  | $ 47 |  |  |  |
General Liability | 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | (34) | 10 | 4 | $ (1) |  |  |  |  |  |  |  |  | $ (21) |  |  |  |  |
General Liability | 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 21 | 9 | $ 2 |  |  |  |  |  |  |  |  | $ 32 |  |  |  |  |  |
General Liability | 2022 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | 2 | $ (1) |  |  |  |  |  |  |  |  | $ 1 |  |  |  |  |  |  |
General Liability | 2023 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cumulative Number of Claims | $ 35 |  |  |  |  |  |  |  |  | $ 35 |  |  |  |  |  |  |  |

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