Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2013 Successor Ambac [Member] Policies	Dec. 31, 2012 Predecessor Ambac [Member] Policies	Jun. 30, 2013 I/SL [Member] Successor Ambac [Member] Policies	Dec. 31, 2012 I/SL [Member] Predecessor Ambac [Member] Policies	Jun. 30, 2013 IA [Member] Successor Ambac [Member] Policies	Dec. 31, 2012 IA [Member] Predecessor Ambac [Member] Policies	Jun. 30, 2013 II [Member] Successor Ambac [Member] Policies	Dec. 31, 2012 II [Member] Predecessor Ambac [Member] Policies	Jun. 30, 2013 III [Member] Successor Ambac [Member] Policies	Dec. 31, 2012 III [Member] Predecessor Ambac [Member] Policies	Jun. 30, 2013 IV [Member] Successor Ambac [Member] Policies	Dec. 31, 2012 IV [Member] Predecessor Ambac [Member] Policies	Jun. 30, 2013 V [Member] Successor Ambac [Member] Policies	Dec. 31, 2012 V [Member] Predecessor Ambac [Member] Policies
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	313	316	16	14	20	12	23	28	91	114	162	147	1	1
Remaining weighted-average contract period (in years)	13 years	13 years	13 years	15 years	18 years	21 years	18 years	18 years	18 years	20 years	10 years	8 years	6 years	6 years
Gross insured contractual payments outstanding:
Principal	$ 21,632,001	$ 24,060,370	$ 844,620	$ 311,157	$ 1,292,048	$ 786,998	$ 1,054,829	$ 1,245,793	$ 6,783,686	$ 9,161,747	$ 11,656,771	$ 12,554,628	$ 47	$ 47
Interest	7,014,447	9,243,183	527,402	166,276	905,512	715,129	521,253	379,237	2,669,245	4,905,775	2,391,017	3,076,746	18	20
Total	28,646,448	33,303,553	1,372,022	477,433	2,197,560	1,502,127	1,576,082	1,625,030	9,452,931	14,067,522	14,047,788	15,631,374	65	67
Gross undiscounted claim liability	11,261,951	12,120,462	8,084	2,135	51,660	40,898	45,137	49,521	3,254,914	4,051,076	7,902,091	7,976,765	65	67
Discount, gross claim liability	(2,235,127)	(2,138,631)	(1,136)	(219)	(5,955)	(3,532)	(13,405)	(3,247)	(1,220,168)	(1,342,910)	(994,459)	(788,720)	(4)	(3)
Gross claim liability before all subrogation and before reinsurance	9,026,824	9,981,831	6,948	1,916	45,705	37,366	31,732	46,274	2,034,746	2,708,166	6,907,632	7,188,045	61	64
Less:
Gross RMBS subrogation	(2,407,276)	(2,561,163)			(407)				(4,867)	(16,170)	(2,402,002)	(2,544,993)
Discount, RMBS subrogation	12,343	37,938			2				18	312	12,323	37,626
Discounted RMBS subrogation, before reinsurance	(2,394,933)	(2,523,225)			(405)				(4,849)	(15,858)	(2,389,679)	(2,507,367)
Less:
Gross other subrogation	(856,302)	(907,729)					(18,826)		(115,254)	(141,012)	(722,222)	(766,717)
Discount, other subrogation	72,069	36,949					8,043		24,666	21,238	39,360	15,711
Discounted other subrogation, before reinsurance	(784,233)	(870,780)					(10,783)		(90,588)	(119,774)	(682,862)	(751,006)
Gross claim liability, net of all subrogation and discounts, before reinsurance	5,847,658	6,587,826	6,948	1,916	45,300	37,366	20,949	46,274	1,939,309	2,572,534	3,835,091	3,929,672	61	64
Less: Unearned premium reserves	(420,429)	(603,794)	(4,627)	(1,179)	(25,561)	(21,626)	(6,436)	(17,120)	(286,503)	(450,247)	(97,302)	(113,622)
Plus: Loss adjustment expenses reserves	114,333	138,108			23		2,438		6,631		105,241	138,108
Claim liability reported on Balance Sheet, before reinsurance	5,541,562	6,122,140	2,321	737	19,762	15,740	16,951	29,154	1,659,437	2,122,287	3,843,030	3,954,158	61	64
Reinsurance recoverable reported on Balance Sheet	$ 154,964	$ 159,086	$ 177		$ 2,620	$ 1,078	$ 4,328	$ 7,085	$ 133,114	$ 128,333	$ 14,725	$ 22,590