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Contingencies - Narrative (Details) - USD ($) $ in Millions | 3 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Loss Contingencies [Line Items] |  |  |  |  |  |
Reinsurance recoverables on asbestos and environmental reserves, net of allowance |  |  | $ 3,419 | $ 3,117 | $ 3,024 | $ 2,942
Property and Casualty Group |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Increase in asbestos and environmental reserves | $ 47 | $ 18 |  |  |  |
Liability for asbestos and environmental reserves |  |  | 555 |  |  |
Former railroad and manufacturing operations |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Increase in asbestos and environmental reserves | $ 21 | $ 11 |  |  |  |
American Premier and its subsidiaries |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |
Liability for environmental and other claims |  |  | 87 |  |  |
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 |  |  | $ 147 |  |  |

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