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, 2022	Dec. 31, 2021
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 23,242	$ 25,112
Insurance Assets	1,842	2,195
Insurance Liabilities	902	1,023
Derivative Liabilities	3
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entities [Line Items]
Derivative Liabilities		5
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	19,204	20,233
Insurance Assets	232	246
Insurance Liabilities	240	257
Derivative Liabilities	0	0
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	4,038	4,879
Insurance Assets	1,610	1,949
Insurance Liabilities	662	765
Derivative Liabilities	3	5
Global Structured Finance [Member] | Residential Mortgage-Backed Securities [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,607	3,265
Insurance Assets	1,594	1,929
Insurance Liabilities	422	521
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other Consumer Asset-Backed [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	706	788
Insurance Assets	14	17
Insurance Liabilities	232	234
Derivative Liabilities	0	0
Global Structured Finance [Member] | Other [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	725	826
Insurance Assets	2	3
Insurance Liabilities	7	10
Derivative Liabilities	$ 3	$ 5