Variable Interest Entities Special Purpose Entities, including Variable Interest Entities - Summary of Assets and Liabilities (Details) $ in Millions	Jun. 30, 2024 USD ($) Entity	Dec. 31, 2023 USD ($) Entity	Jun. 30, 2023 USD ($)
Debt Securities, Available-for-sale, Amortized Cost	$ 2,078	$ 2,197
Fixed maturity securities, at fair value	2,043
Restricted Cash	11	12	$ 10
Derivative assets	18	26
Other assets	163	129
Total assets	8,184	8,428	8,132
Interest Payable	500	475
Long-term debt	515	508
Derivative Liability	26	35
Other Liabilities	203	199
Liabilities	6,748	6,997
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	45	40
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	78	71
Variable Interest Entity, Primary Beneficiary [Member]
Fixed maturity securities, at fair value	2,101	2,167
Restricted Cash	62	246	$ 266
Financing Receivable, after Allowance for Credit Loss	1,567	1,663
Derivative assets	208	226
Other assets	95	92
Total assets	4,033	4,394
Long-term debt	2,599	2,710
Long-term Debt, at par less amortized discount	253	258
Long-term debt	2,853	2,967
Derivative Liability	1,136	1,197
Other Liabilities	7	5
Liabilities	4,048	4,404
Estimated Future Premium Payments Maximum Discounted Rate	52	235
Variable Interest Entity, Primary Beneficiary [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	2,010	2,072
Variable Interest Entity, Primary Beneficiary [Member] | Municipal Bonds [Member]
Debt Securities, Available-for-sale, Amortized Cost	85	88
Fixed maturity securities, at fair value	91	95
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	6	7
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0	0
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member]
Fixed maturity securities, at fair value	2,010	2,072
Restricted Cash	61	245
Financing Receivable, after Allowance for Credit Loss	1,567	1,663
Derivative assets	208	226
Other assets	93	90
Total assets	3,939	4,296
Long-term debt	2,599	2,710
Long-term Debt, at par less amortized discount	97	99
Long-term debt	2,696	2,808
Derivative Liability	1,136	1,197
Cash collateral payable	52
Other Liabilities	6	4
Liabilities	3,890	4,244
Estimated Future Premium Payments Maximum Discounted Rate		235
Variable Interest Entity, Primary Beneficiary [Member] | Ambac UK [Member] | Corporate Debt Securities [Member]
Fixed maturity securities, at fair value	2,010	2,072
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 Assurance [Member]
Fixed maturity securities, at fair value	91	95
Restricted Cash	1	1
Financing Receivable, after Allowance for Credit Loss	0	0
Derivative assets	0	0
Other assets	2	2
Total assets	94	98
Long-term debt	0	0
Long-term Debt, at par less amortized discount	156	159
Long-term debt	156	159
Derivative Liability	0	0
Other Liabilities	1	1
Liabilities	157	160
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	$ 95
Consolidated Entities [Member]
Number Of Consolidated Variable Interest Entities | Entity	6	6
Consolidated Entities [Member] | Ambac UK [Member]
Number Of Consolidated Variable Interest Entities | Entity	4	4
Consolidated Entities [Member] | Ambac Assurance [Member]
Number Of Consolidated Variable Interest Entities | Entity	2	2