Segment Reporting (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) level3FinancialInstruments	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting, Revenue Reconciling Item [Line Items]
Number of Reportable Segments | level3FinancialInstruments	3
Revenues	$ 103	$ 58
Policyholder Benefits and Claims Incurred, Net	(1)	18
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	26	(29)
Provision for income taxes	5	4
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	21	(33)
Premiums Earned, Net	33	14
Net Investment Income	42	34
Amortization of Intangible Assets	12	7
Interest Expense	16	16
Total assets	8,429	8,219	$ 8,428
Premiums Written, Net	28	18
Derivative, Gain (Loss) on Derivative, Net	2	(4)
Insurance Commissions and Fees	18	14
Other Cost and Expense, Operating	35	36
Insurance Commissions	10	8
Depreciation	1	0
Benefits, Losses and Expenses	77	86
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	(1)	(1)
Net income attributable to common shareholders	20	(33)
Realized Investment Gains (Losses)	1	(4)
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	3	1
Other income Items	5	2
Deferred Policy Acquisition Costs, Amortization Expense	4	1
Financial Guarantee
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	53	32
Policyholder Benefits and Claims Incurred, Net	(21)	13
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	25	(32)
Premiums Earned, Net	7	7
Net Investment Income	38	31
Amortization of Intangible Assets	11	6
Interest Expense	16	16
Total assets	7,454	7,503
Derivative, Gain (Loss) on Derivative, Net	2	(3)
Other Cost and Expense, Operating	21	28
Depreciation	0	0
Benefits, Losses and Expenses	28	64
Realized Investment Gains (Losses)	1	(4)
Other income Items	5	2
Deferred Policy Acquisition Costs, Amortization Expense	0	0
Specialty Property & Casualty Program
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	30	9
Policyholder Benefits and Claims Incurred, Net	19	5
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	2	(1)
Premiums Earned, Net	26	7
Net Investment Income	1	1
Total assets	608	349
Other Cost and Expense, Operating	4	4
Depreciation	0	0
Benefits, Losses and Expenses	28	10
Managing General Agency Underwriter
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	18	15
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	4	4
Net Investment Income	0	0
Amortization of Intangible Assets	1	1
Total assets	156	140
Insurance Commissions and Fees	18	14
Other Cost and Expense, Operating	3	2
Insurance Commissions	10	8
Depreciation	0	0
Benefits, Losses and Expenses	14	11
Corporate and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	2	2
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(5)	0
Net Investment Income	2	2
Total assets	211	227
Derivative, Gain (Loss) on Derivative, Net	0	0
Other Cost and Expense, Operating	7	2
Depreciation	0	0
Benefits, Losses and Expenses	7	2
Realized Investment Gains (Losses)	0	0
Other income Items	0	0
Property and Casualty, Commercial Insurance
Segment Reporting, Revenue Reconciling Item [Line Items]
Contractually Specified Servicing Fee, Late Fee, and Ancillary Fee Earned in Exchange for Servicing Financial Asset	3	1
Other income Items	0	0
Deferred Policy Acquisition Costs, Amortization Expense	4	1
Insurance Distribution
Segment Reporting, Revenue Reconciling Item [Line Items]
Other income Items	$ 0	$ 0