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Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended	69 Months Ended
	Sep. 30, 2022	Dec. 31, 2016	Sep. 30, 2022
Asbestos and Environmental
Loss Contingencies [Line Items]
Liability for unpaid losses and loss adjustment expenses, at undiscounted amounts	$ 455		$ 455
Reinsurance Contract [Axis]: Adverse Development Cover Navigators Group
Loss Contingencies [Line Items]
Change in Deferred Gain on Retroactive Reinsurance	209		209
Reinsurance Contract [Axis]: Asbestos and Environmental
Loss Contingencies [Line Items]
Reinsurance, Amount Retained, Per Policy		$ 1,700
Reinsurance Contract [Axis]: Asbestos and Environmental \| Asbestos and Environmental
Loss Contingencies [Line Items]
Change in Deferred Gain on Retroactive Reinsurance	365		365
Reinsurance Retention Policy, Excess Retention, Amount Reinsured			$ 1,015
Reinsurance Contract [Axis]: Asbestos and Environmental \| Asbestos and Environmental \| Remaining [Member]
Loss Contingencies [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Policy	$ 485