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], USD $) In Thousands, unless otherwise specified	Jun. 30, 2013 Successor Ambac [Member]	Dec. 31, 2012 Predecessor Ambac [Member]	Jun. 30, 2013 Global Structured Finance [Member] Successor Ambac [Member]	Dec. 31, 2012 Global Structured Finance [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Global Public Finance [Member] Successor Ambac [Member]	Dec. 31, 2012 Global Public Finance [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Collateralized Debt Obligations [Member] Global Structured Finance [Member] Successor Ambac [Member]	Dec. 31, 2012 Collateralized Debt Obligations [Member] Global Structured Finance [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Residential Mortgage-Backed Securities [Member] Global Structured Finance [Member] Successor Ambac [Member]	Dec. 31, 2012 Residential Mortgage-Backed Securities [Member] Global Structured Finance [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Mortgage-Backed-Commercial [Member] Global Structured Finance [Member] Successor Ambac [Member]	Dec. 31, 2012 Mortgage-Backed-Commercial [Member] Global Structured Finance [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Other Consumer Asset-Backed [Member] Global Structured Finance [Member] Successor Ambac [Member]	Dec. 31, 2012 Other Consumer Asset-Backed [Member] Global Structured Finance [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Other Commercial Asset-Backed [Member] Global Structured Finance [Member] Successor Ambac [Member]	Dec. 31, 2012 Other Commercial Asset-Backed [Member] Global Structured Finance [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Other [Member] Global Structured Finance [Member] Successor Ambac [Member]	Dec. 31, 2012 Other [Member] Global Structured Finance [Member] Predecessor Ambac [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 79,667,048	$ 93,517,995	$ 43,152,587	$ 56,421,767	$ 35,514,461	$ 37,096,228	$ 4,068,252	$ 10,176,522	$ 20,574,099	$ 24,008,616	$ 600,821	$ 643,387	$ 5,601,315	$ 5,895,377	$ 7,856,942	$ 10,192,858	$ 4,451,158	$ 5,505,007
Insurance Assets	1,725,360	1,840,265	1,208,555	1,298,086	516,805	542,179	6,725	9,673	593,246	603,867			90,288	101,494	400,539	451,048	117,757	132,004
Insurance Liabilities	6,604,469	7,463,635	6,009,806	6,830,277	594,663	633,358	10,081	13,328	3,844,796	3,969,336			1,048,836	1,042,522	552,786	1,215,074	553,307	590,017
Derivative Liabilities	$ 215,868	$ 201,434	$ 185,073	$ 172,771	$ 30,795	$ 28,663	$ 109,703	$ 113,057			$ 849	$ 2,418	$ 58,136	$ 45,610	$ 10,627	$ 7,293	$ 5,758	$ 4,393