Insurance Contracts Financial Guarantee Insurance Contracts - Components of Loss and Loss Expense Reserves and Subrogation Recoverable (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Ceded Loss And Loss Expenses Paid Not Yet Recovered		$ 5
Policyholder Benefits and Claims Incurred, Ceded	$ 98	45
Subrogation recoverable	(128)		$ (137)
Claim liability reported on Balance Sheet, before reinsurance	476		559
Liability for Claims and Claims Adjustment Expense	890		893
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables	762	$ 724	756	$ 534
Property and Casualty, Commercial Insurance
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Liability for Claims and Claims Adjustment Expense	286		197
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables	286		197
Present Value of Expected Net Cash Flows- Claims and Loss Expenses [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Subrogation recoverable	7		1
Claim liability reported on Balance Sheet, before reinsurance	676		780
Liability for Claims and Claims Adjustment Expense	669		779
Present Value of Expected Net Cash Flows-Recoveries [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Subrogation recoverable	(136)		(139)
Claim liability reported on Balance Sheet, before reinsurance	(186)		(194)
Liability for Claims and Claims Adjustment Expense	(51)		(55)
Unearned Premium Reserve [Member]
Components of Loss and Loss Expense Reserves and Subrogation Recoverable [Line Items]
Subrogation recoverable	0		0
Claim liability reported on Balance Sheet, before reinsurance	(14)		(28)
Liability for Claims and Claims Adjustment Expense	$ (14)		$ (28)