Variable Interest Entities Special Purpose Entities, including Variable Interest Entities - Summary of Assets and Liabilities (Details) $ in Millions	Jun. 30, 2023 USD ($) Entity	Dec. 31, 2022 USD ($) Entity	Jun. 30, 2022 USD ($)
Debt Securities, Available-for-sale, Amortized Cost	$ 2,033	$ 2,041
Fixed maturity securities, at fair value	1,953
Restricted Cash	10	14	$ 5
Derivative assets	26	27
Other assets	89	84
Total assets	8,132	7,973	10,061
Interest Payable	450	427
Long-term debt	501	639
Derivative Liability	37	38
Other Liabilities	136	163
Liabilities	6,809	6,647
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	30	31
Variable Interest Entity, Primary Beneficiary [Member]
Fixed maturity securities, at fair value	2,056	1,967
Restricted Cash	266	17	$ 2
Financing Receivable, after Allowance for Credit Loss	1,772	1,829
Derivative assets	224	239
Other assets	2	2
Total assets	4,320	4,054
Long-term debt	2,785	2,788
Long-term Debt, at par less amortized discount	171	319
Long-term debt	2,956	3,107
Derivative Liability	1,106	1,048
Other Liabilities	1	5
Liabilities	4,326	4,160
Estimated Future Premium Payments Maximum Discounted Rate	263	0
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	1,952	1,828
Variable Interest Entity, Primary Beneficiary [Member] | Municipal Bonds [Member]
Debt Securities, Available-for-sale, Amortized Cost	99	99
Fixed maturity securities, at fair value	104	96
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0	(4)
Available-for-Sale Securities, Accumulated Gross Unrealized Gain, before Tax	5	1
Variable Interest Entity, Primary Beneficiary [Member] | US States and Political Subdivisions Debt Securities
Fixed maturity securities, at fair value	0	43
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member]
Fixed maturity securities, at fair value	1,952	1,828
Restricted Cash	264	1
Financing Receivable, after Allowance for Credit Loss	1,772	1,829
Derivative assets	224	239
Other assets	0	0
Total assets	4,213	3,896
Long-term debt	2,785	2,788
Long-term Debt, at par less amortized discount	0	0
Long-term debt	2,785	2,788
Derivative Liability	1,106	1,048
Cash collateral payable	263
Other Liabilities	0	0
Liabilities	4,154	3,836
Estimated Future Premium Payments Maximum Discounted Rate		0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	1,952	1,828
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | Municipal Bonds [Member]
Fixed maturity securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | US States and Political Subdivisions Debt Securities
Fixed maturity securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member]
Fixed maturity securities, at fair value	104	139
Restricted Cash	1	16
Financing Receivable, after Allowance for Credit Loss	0	0
Derivative assets	0	0
Other assets	2	2
Total assets	107	157
Long-term debt	0	0
Long-term Debt, at par less amortized discount	171	319
Long-term debt	171	319
Derivative Liability	0	0
Other Liabilities	1	5
Liabilities	172	324
Estimated Future Premium Payments Maximum Discounted Rate	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | Municipal Bonds [Member]
Fixed maturity securities, at fair value	104	96
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | US States and Political Subdivisions Debt Securities
Fixed maturity securities, at fair value	$ 0	$ 43
Consolidated Entities [Member]
Number Of Consolidated Variable Interest Entities | Entity	8	9
Consolidated Entities [Member] | Ambac UK [Member]
Number Of Consolidated Variable Interest Entities | Entity	4	5
Consolidated Entities [Member] | Ambac Assurance [Member]
Number Of Consolidated Variable Interest Entities | Entity	4	4