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	3 Months Ended	12 Months Ended
	Mar. 31, 2015 Policies	Dec. 31, 2014 Policies	Mar. 31, 2014	Dec. 31, 2013
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	330	325
Remaining weighted-average contract period (in years)	15 years	16 years
Gross insured contractual payments outstanding:
Principal	$ 18,482,283	$ 18,322,914
Interest	13,218,716	7,254,995
Total	31,700,999	25,577,909
Gross undiscounted claim liability	8,232,073	8,679,974
Discount, gross claim liability	1,260,130	1,509,948
Gross claim liability before all subrogation and before reinsurance	6,971,943	7,170,026
Less:
Gross RMBS subrogation	(2,579,450)	(2,541,219)
Discount, RMBS subrogation	11,097	17,679
Discounted RMBS subrogation, before reinsurance	(2,568,353)	(2,523,540)	(2,224,295)	(2,206,598)
Less:
Gross other subrogation	(815,033)	(792,287)
Discount, other subrogation	76,537	91,808
Discounted other subrogation, before reinsurance	(738,496)	(700,479)
Gross claim liability, net of all subrogation and discounts, before reinsurance	3,665,094	3,946,007
Less: Unearned premium reserves	(258,765)	(241,348)
Plus: Loss adjustment expenses reserves	85,533	94,074
Claim liability reported on Balance Sheet, before reinsurance	3,491,862	3,798,733
Reinsurance recoverable reported on Balance Sheet	79,308	99,838
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	34	36
Remaining weighted-average contract period (in years)	7 years	8 years
Gross insured contractual payments outstanding:
Principal	910,033	1,026,513
Interest	339,721	418,746
Total	1,249,754	1,445,259
Gross undiscounted claim liability	12,901	16,360
Discount, gross claim liability	644	1,147
Gross claim liability before all subrogation and before reinsurance	12,257	15,213
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	12,257	15,213
Less: Unearned premium reserves	(8,812)	(10,945)
Plus: Loss adjustment expenses reserves	0	3
Claim liability reported on Balance Sheet, before reinsurance	3,445	4,271
Reinsurance recoverable reported on Balance Sheet	1	73
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	21	26
Remaining weighted-average contract period (in years)	16 years	12 years
Gross insured contractual payments outstanding:
Principal	399,516	519,291
Interest	159,138	212,296
Total	558,654	731,587
Gross undiscounted claim liability	6,344	11,525
Discount, gross claim liability	605	937
Gross claim liability before all subrogation and before reinsurance	5,739	10,588
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	5,739	10,588
Less: Unearned premium reserves	(2,175)	(3,432)
Plus: Loss adjustment expenses reserves	16	1,303
Claim liability reported on Balance Sheet, before reinsurance	3,580	8,459
Reinsurance recoverable reported on Balance Sheet	910	890
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	43	33
Remaining weighted-average contract period (in years)	17 years	15 years
Gross insured contractual payments outstanding:
Principal	4,186,210	3,091,744
Interest	8,484,779	1,878,770
Total	12,670,989	4,970,514
Gross undiscounted claim liability	239,113	155,488
Discount, gross claim liability	18,502	16,438
Gross claim liability before all subrogation and before reinsurance	220,611	139,050
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(12,388)	(18,034)
Discount, other subrogation	3,474	6,069
Discounted other subrogation, before reinsurance	(8,914)	(11,965)
Gross claim liability, net of all subrogation and discounts, before reinsurance	211,697	127,085
Less: Unearned premium reserves	(107,836)	(73,749)
Plus: Loss adjustment expenses reserves	2,185	1,968
Claim liability reported on Balance Sheet, before reinsurance	106,046	55,304
Reinsurance recoverable reported on Balance Sheet	2,331	1,355
III [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	66	69
Remaining weighted-average contract period (in years)	21 years	21 years
Gross insured contractual payments outstanding:
Principal	3,550,121	3,792,559
Interest	2,286,780	2,765,537
Total	5,836,901	6,558,096
Gross undiscounted claim liability	1,596,918	2,040,402
Discount, gross claim liability	521,225	716,812
Gross claim liability before all subrogation and before reinsurance	1,075,693	1,323,590
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(142,548)	(127,143)
Discount, other subrogation	35,608	36,779
Discounted other subrogation, before reinsurance	(106,940)	(90,364)
Gross claim liability, net of all subrogation and discounts, before reinsurance	968,753	1,233,226
Less: Unearned premium reserves	(76,061)	(88,332)
Plus: Loss adjustment expenses reserves	7,465	6,470
Claim liability reported on Balance Sheet, before reinsurance	900,157	1,151,364
Reinsurance recoverable reported on Balance Sheet	85,082	110,957
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	163	160
Remaining weighted-average contract period (in years)	13 years	12 years
Gross insured contractual payments outstanding:
Principal	9,376,691	9,892,760
Interest	1,928,647	1,979,627
Total	11,305,338	11,872,387
Gross undiscounted claim liability	6,297,440	6,456,139
Discount, gross claim liability	712,562	774,611
Gross claim liability before all subrogation and before reinsurance	5,584,878	5,681,528
Less:
Gross RMBS subrogation	(2,579,450)	(2,541,219)
Discount, RMBS subrogation	11,097	17,679
Discounted RMBS subrogation, before reinsurance	(2,568,353)	(2,523,540)
Less:
Gross other subrogation	(646,741)	(647,110)
Discount, other subrogation	33,795	48,960
Discounted other subrogation, before reinsurance	(612,946)	(598,150)
Gross claim liability, net of all subrogation and discounts, before reinsurance	2,403,579	2,559,838
Less: Unearned premium reserves	(63,368)	(64,890)
Plus: Loss adjustment expenses reserves	75,825	84,330
Claim liability reported on Balance Sheet, before reinsurance	2,416,036	2,579,278
Reinsurance recoverable reported on Balance Sheet	(9,016)	(13,437)
V [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies	3	1
Remaining weighted-average contract period (in years)	6 years	6 years
Gross insured contractual payments outstanding:
Principal	59,712	47
Interest	19,651	19
Total	79,363	66
Gross undiscounted claim liability	79,357	60
Discount, gross claim liability	6,592	3
Gross claim liability before all subrogation and before reinsurance	72,765	57
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(13,356)	0
Discount, other subrogation	3,660	0
Discounted other subrogation, before reinsurance	(9,696)	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	63,069	57
Less: Unearned premium reserves	(513)	0
Plus: Loss adjustment expenses reserves	42	0
Claim liability reported on Balance Sheet, before reinsurance	62,598	57
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0