Variable Interest Entities Special Purpose Entities, including Variable Interest Entities - Summary of Assets and Liabilities (Details) $ in Millions	Sep. 30, 2023 USD ($) Entity	Dec. 31, 2022 USD ($) Entity	Sep. 30, 2022 USD ($)
Debt Securities, Available-for-sale, Amortized Cost	$ 2,100	$ 2,041
Fixed maturity securities, at fair value	2,004
Restricted Cash	13	14	$ 6
Derivative assets	15	27
Other assets	94	84
Total assets	7,847	7,973	9,412
Interest Payable	462	427
Long-term debt	505	639
Derivative Liability	22	38
Other Liabilities	168	163
Liabilities	6,507	6,647
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	27	31
Variable Interest Entity, Primary Beneficiary [Member]
Fixed maturity securities, at fair value	1,948	1,967
Restricted Cash	256	17	$ 2
Financing Receivable, after Allowance for Credit Loss	1,551	1,829
Derivative assets	219	239
Other assets	1	2
Total assets	3,976	4,054
Long-term debt	2,535	2,788
Long-term Debt, at par less amortized discount	164	319
Long-term debt	2,699	3,107
Derivative Liability	1,038	1,048
Other Liabilities	1	5
Liabilities	3,992	4,160
Estimated Future Premium Payments Maximum Discounted Rate	254	0
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	1,857	1,828
Variable Interest Entity, Primary Beneficiary [Member] | Municipal Bonds [Member]
Debt Securities, Available-for-sale, Amortized Cost	94	99
Fixed maturity securities, at fair value	91	96
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(4)	(4)
Available-for-Sale Securities, Accumulated Gross Unrealized Gain, before Tax	1	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	1,857	1,828
Restricted Cash	255	1
Financing Receivable, after Allowance for Credit Loss	1,551	1,829
Derivative assets	219	239
Other assets	0	0
Total assets	3,883	3,896
Long-term debt	2,535	2,788
Long-term Debt, at par less amortized discount	0	0
Long-term debt	2,535	2,788
Derivative Liability	1,038	1,048
Cash collateral payable	254
Other Liabilities	0	0
Liabilities	3,827	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	1,857	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	91	139
Restricted Cash	1	16
Financing Receivable, after Allowance for Credit Loss	0	0
Derivative assets	0	0
Other assets	1	2
Total assets	94	157
Long-term debt	0	0
Long-term Debt, at par less amortized discount	164	319
Long-term debt	164	319
Derivative Liability	0	0
Other Liabilities	0	5
Liabilities	165	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	91	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	7	9
Consolidated Entities [Member] | Ambac UK [Member]
Number Of Consolidated Variable Interest Entities | Entity	3	5
Consolidated Entities [Member] | Ambac Assurance [Member]
Number Of Consolidated Variable Interest Entities | Entity	4	4