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, 2023	Dec. 31, 2022
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 21,484	$ 21,639
Insurance Assets	361	490
Insurance Liabilities	877	840
Derivative Liabilities	0
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Derivative Liabilities		1
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	17,981	17,997
Insurance Assets	218	216
Insurance Liabilities	215	212
Derivative Liabilities	0	0
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	3,503	3,642
Insurance Assets	142	274
Insurance Liabilities	662	628
Derivative Liabilities	0	1
Global Structured Finance [Member] | Residential Mortgage-Backed Securities [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,475	2,559
Insurance Assets	135	266
Insurance Liabilities	434	400
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other Consumer Asset-Backed [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	595	652
Insurance Assets	5	6
Insurance Liabilities	226	225
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	432	430
Insurance Assets	2	2
Insurance Liabilities	2	2
Derivative Liabilities	$ 0	$ 1