Special Purpose Entities, Including Variable Interest Entities - Summary of Carrying Amount of Assets, Liabilities and Maximum Exposure to Loss of Ambac's Variable Interests in Non-Consolidated Variable Interest Entities (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 20,109	$ 20,861
Insurance Assets	331	351
Insurance Liabilities	742	836
Derivative Liabilities	0
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Derivative Liabilities		0
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	17,101	17,498
Insurance Assets	204	209
Insurance Liabilities	196	202
Derivative Liabilities	0	0
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	3,007	3,364
Insurance Assets	127	141
Insurance Liabilities	546	634
Derivative Liabilities	0	0
Global Structured Finance [Member] | Residential Mortgage-Backed Securities [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,224	2,391
Insurance Assets	123	135
Insurance Liabilities	409	432
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other Consumer Asset-Backed [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	365	540
Insurance Assets	3	5
Insurance Liabilities	135	200
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	418	433
Insurance Assets	2	2
Insurance Liabilities	2	2
Derivative Liabilities	$ 0	$ 0