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	Mar. 31, 2015	Dec. 31, 2014
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 61,759,766
Insurance Assets	1,755,687
Insurance Liabilities	4,757,836
Derivative Liabilities	(204,040)
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	31,085,114
Insurance Assets	1,316,835
Insurance Liabilities	4,244,172
Derivative Liabilities	(174,149)
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	30,674,652	31,639,004
Insurance Assets	438,852	457,774
Insurance Liabilities	513,664	533,192
Derivative Liabilities	(29,891)	(22,135)
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,297,393	1,386,100
Insurance Assets	303	345
Insurance Liabilities	3,889	4,000
Derivative Liabilities	(155,357)	(145,565)
Residential Mortgage-Backed Securities [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	18,837,405	19,464,549
Insurance Assets	1,037,566	1,011,888
Insurance Liabilities	2,879,199	2,924,987
Other Consumer Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	4,460,126	5,109,776
Insurance Assets	55,219	65,204
Insurance Liabilities	671,303	885,572
Derivative Liabilities	(35,558)	(36,877)
Other Commercial Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,943,920	3,119,891
Insurance Assets	129,218	135,215
Insurance Liabilities	124,124	128,988
Derivative Liabilities	0	0
Other [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	3,546,270	3,801,382
Insurance Assets	94,529	97,345
Insurance Liabilities	565,657	599,915
Derivative Liabilities	$ 16,766	$ 18,176