Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Loss And Loss Adjustment Expense Reserves [Line Items]
Impact of VIE Consolidation on Gross Loss and Loss Reserves	$ 0	$ 292
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance of net loss and loss expense reserves	419	(578)
Current Year Claims and Claims Adjustment Expense	20	6
Prior Year Claims and Claims Adjustment Expense	(71)	(347)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	(51)	(341)
Claim and loss expense payments, net of subrogation and reinsurance	(2)	1
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	139	195
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	(137)	(195)
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss)	0	(3)
Liability for Unpaid Claims and Claims Adjustment Expense, Net	506	(727)	$ 419	$ (578)
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	165	79	115	56
Policyholder Benefits and Claims Incurred, Ceded	75	30
Net Incurred RMBS Subrogation Recoveries	0	(80)
Ceded Loss And Loss Expenses Paid Not Yet Recovered		1
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables	670	$ (940)	534	$ (522)
Financial Guarantee
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	0		0
Loss Reserves Ceded To Reinsurers	$ 32		$ 33