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Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
Contingencies - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Reinsurance recoverables on asbestos and environmental reserves, net of allowance		$ 3,767	$ 3,419	$ 3,117	$ 3,024
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration]		Other liabilities
Property and Casualty Group
Loss Contingencies [Line Items]
Increase in asbestos and environmental reserves	$ 47
Liability for asbestos and environmental reserves		$ 525
Former railroad and manufacturing operations
Loss Contingencies [Line Items]
Liability for Asbestos and Environmental Claims, Net, Period Increase (Decrease)	$ 21
American Premier and its subsidiaries
Loss Contingencies [Line Items]
Liability for environmental and other claims		89
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		$ 140