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Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended	87 Months Ended
	Mar. 31, 2024	Dec. 31, 2016	Mar. 31, 2024	Dec. 31, 2023
Reinsurance Contract [Axis]: Adverse Development Cover Navigators Group
Loss Contingencies [Line Items]
Change in Deferred Gain on Retroactive Reinsurance	$ 185		$ 185	$ 209
Asbestos and Environmental
Loss Contingencies [Line Items]
Liability for unpaid losses and loss adjustment expenses, at undiscounted amounts	216		216
Asbestos and Environmental \| Reinsurance Contract [Axis]: Asbestos and Environmental
Loss Contingencies [Line Items]
Change in Deferred Gain on Retroactive Reinsurance	788		788
Reinsurance, Amount Retained, Per Policy		$ 1,700
Reinsurance Retention Policy, Excess Retention, Amount Reinsured			$ 1,438
Asbestos and Environmental \| Reinsurance Contract [Axis]: Asbestos and Environmental \| Remaining [Member]
Loss Contingencies [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Policy	$ 62