Reserve for Unpaid Losses and Loss Adjustment Expenses - PC Additional Information (Details) - USD ($) $ in Millions		3 Months Ended
	Apr. 20, 2023	Mar. 31, 2024	Dec. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability for Claims and Claims Adjustment Expense		$ 42,771	$ 42,318
Reinsurance Recoverables, Gross		7,195	7,207
Abuse Claims | General Liability [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability for Claims and Claims Adjustment Expense		787
Prior accident years	$ 787
Reinsurance Contract [Axis]: Adverse Development Cover Navigators Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Change in Deferred Gain on Retroactive Reinsurance		185	$ 209
Reinsurance Contract [Axis]: Asbestos and Environmental | Asbestos and Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Change in Deferred Gain on Retroactive Reinsurance		788
Maximum | Reinsurance Contract [Axis]: Adverse Development Cover Navigators Group
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Policy		300
Maximum | Reinsurance Contract [Axis]: Asbestos and Environmental | Asbestos and Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance, Excess Retention, Amount Reinsured, Per Policy		$ 1,500