Contingencies - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
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