Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 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	18	2
Prior Year Claims and Claims Adjustment Expense	(19)	16
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	(1)	18
Claim and loss expense payments, net of subrogation and reinsurance	(1)	0
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	(55)	141
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	56	(141)
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss)	0	0
Liability for Unpaid Claims and Claims Adjustment Expense, Net	513	578	$ 570	$ 419
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments	208	127	186	115
Policyholder Benefits and Claims Incurred, Ceded	35	20
Ceded Loss And Loss Expenses Paid Not Yet Recovered		3
Liability for Claim and Claim Adjustment Expenses Net of Subrogation recoverables	721	$ 705	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