Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning balance of net loss and loss expense reserves	$ 570	$ 419
Current Year Claims and Claims Adjustment Expense	60	20
Prior Year Claims and Claims Adjustment Expense	(6)	(71)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	54	(51)
Claim and loss expense payments, net of subrogation and reinsurance	(10)	(2)
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	(68)	139
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	78	(137)
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss)	(1)	0
Liability for Unpaid Claims and Claims Adjustment Expense, Net	545	506	$ 570	$ 419
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	269	165	186	115
Policyholder Benefits and Claims Incurred, Ceded	74	75
Ceded Loss And Loss Expenses Paid Not Yet Recovered		7
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables	814	$ 670	756	$ 534
Financial Guarantee
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Ceded Loss And Loss Expenses Paid Not Yet Recovered	1		(1)
Loss Reserves Ceded To Reinsurers	$ 26		$ 30