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 (Detail) (Variable Interest Entity [Member], Successor [Member], USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 61,258,561	$ 74,292,628
Insurance Assets	1,767,771	1,728,422
Insurance Liabilities	5,076,654	6,662,385
Derivative Liabilities	(186,401)	(161,408)
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	29,619,557	38,559,770
Insurance Assets	1,309,997	1,196,903
Insurance Liabilities	4,543,462	6,058,046
Derivative Liabilities	(164,266)	(134,296)
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	31,639,004	35,732,858
Insurance Assets	457,774	531,519
Insurance Liabilities	533,192	604,339
Derivative Liabilities	(22,135)	(27,112)
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,386,100	2,317,612
Insurance Assets	345	3,867
Insurance Liabilities	4,000	7,119
Derivative Liabilities	(145,565)	(102,704)
Residential Mortgage-Backed Securities [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	16,202,408	19,231,335
Insurance Assets	1,011,888	581,498
Insurance Liabilities	2,924,987	3,890,937
Other Consumer Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	5,109,776	5,425,583
Insurance Assets	65,204	68,511
Insurance Liabilities	885,572	992,177
Derivative Liabilities	(36,877)	(39,916)
Other Commercial Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	3,119,891	7,237,953
Insurance Assets	135,215	429,559
Insurance Liabilities	128,988	559,600
Derivative Liabilities	0	0
Other [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	3,801,382	4,347,287
Insurance Assets	97,345	113,468
Insurance Liabilities	599,915	608,213
Derivative Liabilities	$ 18,176	$ 8,324