Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Detail) (Successor [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Policies	Dec. 31, 2013 Policies	Apr. 30, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	325	339
Remaining weighted-average contract period (in years)	16 years	14 years
Gross insured contractual payments outstanding:
Principal	$ 18,322,914	$ 22,206,789
Interest	7,254,995	8,397,133
Total	25,577,909	30,603,922
Gross undiscounted claim liability	8,679,974	11,276,259
Discount, gross claim liability	1,509,948	2,452,448
Gross claim liability before all subrogation and before reinsurance	7,170,026	8,823,811
Less:
Gross RMBS subrogation	(2,541,219)	(2,215,849)
Discount, RMBS subrogation	17,679	9,251
Discounted RMBS subrogation, before reinsurance	(2,523,540)	(2,206,598)	(2,482,918)	(2,523,225)	(2,720,266)
Less:
Gross other subrogation	(792,287)	(846,699)
Discount, other subrogation	91,808	91,313
Discounted other subrogation, before reinsurance	(700,479)	(755,386)
Gross claim liability, net of all subrogation and discounts, before reinsurance	3,946,007	5,861,827
Less: Unearned premium reserves	(241,348)	(502,984)
Plus: Loss adjustment expenses reserves	94,074	111,391
Claim liability reported on Balance Sheet, before reinsurance	3,798,733	5,470,234
Reinsurance recoverable reported on Balance Sheet	99,838	121,249
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	36	18
Remaining weighted-average contract period (in years)	8 years	13 years
Gross insured contractual payments outstanding:
Principal	1,026,513	834,708
Interest	418,746	506,903
Total	1,445,259	1,341,611
Gross undiscounted claim liability	16,360	7,447
Discount, gross claim liability	1,147	1,225
Gross claim liability before all subrogation and before reinsurance	15,213	6,222
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	15,213	6,222
Less: Unearned premium reserves	(10,945)	(4,060)
Plus: Loss adjustment expenses reserves	3	0
Claim liability reported on Balance Sheet, before reinsurance	4,271	2,162
Reinsurance recoverable reported on Balance Sheet	73	146
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	26	23
Remaining weighted-average contract period (in years)	12 years	19 years
Gross insured contractual payments outstanding:
Principal	519,291	1,125,284
Interest	212,296	871,751
Total	731,587	1,997,035
Gross undiscounted claim liability	11,525	54,398
Discount, gross claim liability	937	6,726
Gross claim liability before all subrogation and before reinsurance	10,588	47,672
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	10,588	47,672
Less: Unearned premium reserves	(3,432)	(22,901)
Plus: Loss adjustment expenses reserves	1,303	11
Claim liability reported on Balance Sheet, before reinsurance	8,459	24,782
Reinsurance recoverable reported on Balance Sheet	890	2,271
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	33	52
Remaining weighted-average contract period (in years)	15 years	17 years
Gross insured contractual payments outstanding:
Principal	3,091,744	3,464,420
Interest	1,878,770	2,130,271
Total	4,970,514	5,594,691
Gross undiscounted claim liability	155,488	221,321
Discount, gross claim liability	16,438	32,630
Gross claim liability before all subrogation and before reinsurance	139,050	188,691
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(18,034)	(20,367)
Discount, other subrogation	6,069	9,522
Discounted other subrogation, before reinsurance	(11,965)	(10,845)
Gross claim liability, net of all subrogation and discounts, before reinsurance	127,085	177,846
Less: Unearned premium reserves	(73,749)	(95,550)
Plus: Loss adjustment expenses reserves	1,968	2,257
Claim liability reported on Balance Sheet, before reinsurance	55,304	84,553
Reinsurance recoverable reported on Balance Sheet	1,355	2,273
III [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	69	76
Remaining weighted-average contract period (in years)	21 years	19 years
Gross insured contractual payments outstanding:
Principal	3,792,559	5,597,387
Interest	2,765,537	2,331,222
Total	6,558,096	7,928,609
Gross undiscounted claim liability	2,040,402	3,029,891
Discount, gross claim liability	716,812	1,299,032
Gross claim liability before all subrogation and before reinsurance	1,323,590	1,730,859
Less:
Gross RMBS subrogation	0	(4,516)
Discount, RMBS subrogation	0	15
Discounted RMBS subrogation, before reinsurance	0	(4,501)
Less:
Gross other subrogation	(127,143)	(116,145)
Discount, other subrogation	36,779	36,125
Discounted other subrogation, before reinsurance	(90,364)	(80,020)
Gross claim liability, net of all subrogation and discounts, before reinsurance	1,233,226	1,646,338
Less: Unearned premium reserves	(88,332)	(280,245)
Plus: Loss adjustment expenses reserves	6,470	1,658
Claim liability reported on Balance Sheet, before reinsurance	1,151,364	1,367,751
Reinsurance recoverable reported on Balance Sheet	110,957	119,795
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	160	169
Remaining weighted-average contract period (in years)	12 years	11 years
Gross insured contractual payments outstanding:
Principal	9,892,760	11,184,943
Interest	1,979,627	2,556,968
Total	11,872,387	13,741,911
Gross undiscounted claim liability	6,456,139	7,963,137
Discount, gross claim liability	774,611	1,112,829
Gross claim liability before all subrogation and before reinsurance	5,681,528	6,850,308
Less:
Gross RMBS subrogation	(2,541,219)	(2,211,333)
Discount, RMBS subrogation	17,679	9,236
Discounted RMBS subrogation, before reinsurance	(2,523,540)	(2,202,097)
Less:
Gross other subrogation	(647,110)	(710,187)
Discount, other subrogation	48,960	45,666
Discounted other subrogation, before reinsurance	(598,150)	(664,521)
Gross claim liability, net of all subrogation and discounts, before reinsurance	2,559,838	3,983,690
Less: Unearned premium reserves	(64,890)	(100,228)
Plus: Loss adjustment expenses reserves	84,330	107,465
Claim liability reported on Balance Sheet, before reinsurance	2,579,278	3,990,927
Reinsurance recoverable reported on Balance Sheet	(13,437)	(3,236)
V [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	1	1
Remaining weighted-average contract period (in years)	6 years	6 years
Gross insured contractual payments outstanding:
Principal	47	47
Interest	19	18
Total	66	65
Gross undiscounted claim liability	60	65
Discount, gross claim liability	3	6
Gross claim liability before all subrogation and before reinsurance	57	59
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	57	59
Less: Unearned premium reserves	0	0
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	57	59
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0