Variable Interest Entities Special Purpose Entities, including Variable Interest Entities - Summary of Assets and Liabilities (Details) $ in Millions	Mar. 31, 2023 USD ($) Entity	Dec. 31, 2022 USD ($) Entity	Mar. 31, 2022 USD ($)
Debt Securities, Available-for-sale, Amortized Cost	$ 1,983	$ 2,041
Fixed maturity securities, at fair value	1,923
Restricted Cash	10	14	$ 7
Derivative assets	31	27
Other assets	85	84
Total assets	8,219	7,973	11,531
Interest Payable	438	427
Long-term debt	497	639
Derivative Liability	44	38
Other Liabilities	141	163
Liabilities	6,892	6,647
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	31	31
Variable Interest Entity, Primary Beneficiary [Member]
Fixed maturity securities, at fair value	2,119	1,967
Restricted Cash	256	17	$ 49
Financing Receivable, after Allowance for Credit Loss	1,856	1,829
Derivative assets	243	239
Other assets	1	2
Total assets	4,476	4,054
Long-term debt	2,869	2,788
Long-term Debt, at par less amortized discount	191	319
Long-term debt	3,060	3,107
Derivative Liability	1,174	1,048
Other Liabilities	1	5
Liabilities	4,489	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	2,003	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	100	96
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(1)	(4)
Available-for-Sale Securities, Accumulated Gross Unrealized Gain, before Tax	2	1
Variable Interest Entity, Primary Beneficiary [Member] | US States and Political Subdivisions Debt Securities
Fixed maturity securities, at fair value	16	43
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member]
Fixed maturity securities, at fair value	2,003	1,828
Restricted Cash	255	1
Financing Receivable, after Allowance for Credit Loss	1,856	1,829
Derivative assets	243	239
Other assets	0	0
Total assets	4,358	3,896
Long-term debt	2,869	2,788
Long-term Debt, at par less amortized discount	0	0
Long-term debt	2,869	2,788
Derivative Liability	1,174	1,048
Cash collateral payable	254
Other Liabilities	0	0
Liabilities	4,297	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	2,003	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	116	139
Restricted Cash	1	16
Financing Receivable, after Allowance for Credit Loss	0	0
Derivative assets	0	0
Other assets	1	2
Total assets	118	157
Long-term debt	0	0
Long-term Debt, at par less amortized discount	191	319
Long-term debt	191	319
Derivative Liability	0	0
Other Liabilities	1	5
Liabilities	192	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	100	96
Variable Interest Entity, Primary Beneficiary [Member] | Ambac Assurance [Member] | US States and Political Subdivisions Debt Securities
Fixed maturity securities, at fair value	$ 16	$ 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