Special Purpose Entities, Including Variable Interest Entities - Additional Information (Details)	3 Months Ended
	Mar. 31, 2022 USD ($) consolidationVIE Entity	Mar. 31, 2021 USD ($) consolidationVIE	Dec. 31, 2021 USD ($) Entity
Variable Interest Entities [Line Items]
Variable Interest Entity Change in Fair Value of Assets and Liabilities	$ (1,000,000)	$ (1,000,000)
Realized Investment Gains (Losses)	10,000,000	2,000,000
Other Operating Income (Expense), Net	2,000,000	(2,000,000)
Fair value of special purpose entities	0
Variable Interest Entity, Measure of Activity, Income or Loss before Tax	22,000,000	$ 0
Long-term debt	$ 2,242,000,000		$ 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	$ 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		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)	1,000,000
VIE Change in FV of Assets Liabilities, Net of Credit Risk Change	(1,000,000)	(1,000,000)
Gross Investment Income, Operating	(4,000,000)	2,000,000
Interest Expense, Long-term Debt	(2,000,000)	(1,000,000)
Long-term debt	$ 4,124,000,000		$ 4,216,000,000
Ambac UK [Member] | Consolidated Entities [Member]
Variable Interest Entities [Line Items]
Number Of Consolidated Variable Interest Entities | Entity	5		5
Ambac UK [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Long-term debt	$ 3,701,000,000		$ 4,056,000,000
Fixed Income Investments [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Realized Investment Gains (Losses)	$ 1,000,000	$ 1,000,000