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Contingencies - Narrative (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
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Loss Contingencies [Line Items] |  |  |  |
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration] | Other Liabilities |  |  |
Reinsurance recoverables on asbestos and environmental reserves, net of allowance | $ 4,288 | $ 3,767 | $ 3,419 | $ 3,117
Property and Casualty Group |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Liability for asbestos and environmental reserves | 498 |  |  |
American Premier and its subsidiaries |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Liability for environmental and other claims | 94 |  |  |
GAFRI |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Liability for environmental and other claims | 7 |  |  |
A&E reserves | Property and Casualty Group |  |  |  |
Loss Contingencies [Line Items] |  |  |  |
Reinsurance recoverables on asbestos and environmental reserves, net of allowance | $ 128 |  |  |

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