Special Purpose Entities, Including Variable Interest Entities - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2022 USD ($) consolidationVIE Entity	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) Entity	Sep. 30, 2021 USD ($) consolidationVIE	Dec. 31, 2021 USD ($) Entity
Variable Interest Entities [Line Items]
Variable Interest Entity Change in Fair Value of Assets and Liabilities	$ (3,000,000)	$ 2,000,000	$ (2,000,000)	$ 2,000,000
Realized Investment Gains (Losses)	14,000,000	3,000,000	31,000,000	4,000,000
Other Operating Income (Expense), Net	1,000,000	1,000,000	5,000,000	0
Fair value of special purpose entities	0		0
Variable Interest Entity, Measure of Activity, Income or Loss before Tax	(1,000,000)	3,000,000	14,000,000	$ 5,000,000
Long-term debt	$ 2,201,000,000		$ 2,201,000,000		$ 2,230,000,000
Number of Variable Interest Entities Consolidated During the Period			2	0
Number of Variable Interest Entities Deconsolidated During Period | consolidationVIE	0			0
Gain (loss) from consolidating VIEs	$ 0	0	$ 28,000,000	$ 0
Number of Trusts Established Resulting From Puerto Rico Restructuring Transaction			2
Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number Of Consolidated Variable Interest Entities | Entity	8		8		6
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, before Tax	$ 1,000,000	0	$ (1,000,000)	1,000,000
VIE Change in FV of Assets Liabilities, Net of Credit Risk Change	(2,000,000)	2,000,000	(3,000,000)	3,000,000
Gross Investment Income, Operating	1,000,000	1,000,000
Interest Expense, Long-term Debt	(1,000,000)	(1,000,000)	(8,000,000)	(4,000,000)
Long-term debt	$ 2,752,000,000		$ 2,752,000,000		$ 4,216,000,000
Ambac UK [Member] | Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number Of Consolidated Variable Interest Entities | Entity	5		5		5
Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Long-term debt	$ 2,603,000,000		$ 2,603,000,000		$ 4,056,000,000
Ambac Assurance [Member] | Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number Of Consolidated Variable Interest Entities | Entity	3		3		1
Ambac Assurance [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Long-term debt	$ 149,000,000		$ 149,000,000		$ 160,000,000
Fixed Income Investments [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Gross Investment Income, Operating			(4,000,000)	5,000,000
Realized Investment Gains (Losses)	1,000,000	$ 1,000,000	2,000,000	$ 2,000,000
Sitka AAC Note | Ambac Assurance Corporation [Member]
Variable Interest Entities [Line Items]
Long-term debt	1,157,000,000		1,157,000,000		1,154,000,000
Sitka AAC Note | Ambac Assurance [Member]
Variable Interest Entities [Line Items]
Long-term debt	$ 87,000,000		$ 87,000,000		$ 0