Reserves for Insurance Losses and Loss Adjustment Expenses (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]
Gross reserves for insurance losses and loss adjustment expenses, beginning balance	$ 140	$ 119
Less: Reinsurance recoverable	66	72
Net reserves for insurance losses and loss adjustment expenses	87	58	$ 74	$ 47
Current year	103	87
Prior years	9	1
Total net insurance losses and loss adjustment expenses incurred	112	88
Current year	(57)	(49)
Prior years	(42)	(28)
Total net insurance losses and loss adjustment expenses paid or payable	(99)	(77)
Plus: Reinsurance recoverable	77	75
Gross reserves for insurance losses and loss adjustment expenses, ending balance	$ 164	$ 133