Losses and Loss Expense Reserve (Details 1) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2012 Policy	Dec. 31, 2011 Policy
Summary of information related to policies currently included in Ambac's loss reserves
Number of policies	353	330
Remaining weighted-average contract period (in years)	14 years	13 years
Gross insured contractual payments outstanding:
Principal	$ 27,592,365	$ 31,072,226
Interest	11,929,208	13,963,359
Total	39,521,573	45,035,585
Gross undiscounted claim liability	13,232,698	12,511,194
Discount, gross claim liability	(2,046,050)	(2,279,109)
Gross claim liability before all subrogation and before reinsurance	11,186,648	10,232,085
Less:
Gross RMBS subrogation	(2,813,551)	(2,778,645)
Discount, RMBS subrogation	43,360	58,379
Subrogation recoveries	(2,770,191)	(2,720,266)
Less:
Gross other subrogation	(865,457)	(720,871)
Discount, other subrogation	33,396	52,539
Discounted other subrogation, before reinsurance	(832,060)	(668,332)
Gross claim liability, net of all subrogation and discounts, before reinsurance	7,584,396	6,843,487
Less: Unearned premium reserves	(558,702)	(546,520)
Plus: Loss adjustment expenses reserves	139,872	87,294
Claim liability reported on Balance Sheet, before reinsurance	7,165,566	6,384,261
Reinsurance recoverable reported on Balance Sheet	169,961	159,902
I/SL [Member]
Summary of information related to policies currently included in Ambac's loss reserves
Number of policies	29	27
Remaining weighted-average contract period (in years)	21 years	18 years
Gross insured contractual payments outstanding:
Principal	1,471,818	2,222,493
Interest	904,999	1,069,538
Total	2,376,817	3,292,031
Gross undiscounted claim liability	43,445	48,573
Discount, gross claim liability	(3,686)	(4,208)
Gross claim liability before all subrogation and before reinsurance	39,759	44,365
Less:
Gross RMBS subrogation
Discount, RMBS subrogation
Subrogation recoveries
Less:
Gross other subrogation
Discount, other subrogation
Discounted other subrogation, before reinsurance
Gross claim liability, net of all subrogation and discounts, before reinsurance	39,759	44,365
Less: Unearned premium reserves	(21,956)	(25,264)
Plus: Loss adjustment expenses reserves
Claim liability reported on Balance Sheet, before reinsurance	17,803	19,101
Reinsurance recoverable reported on Balance Sheet	2,124	1,117
IA [Member]
Summary of information related to policies currently included in Ambac's loss reserves
Number of policies	9	10
Remaining weighted-average contract period (in years)	10 years	10 years
Gross insured contractual payments outstanding:
Principal	149,122	354,713
Interest	72,942	100,448
Total	222,064	455,161
Gross undiscounted claim liability	34,536	10,667
Discount, gross claim liability	(3,690)	(2,316)
Gross claim liability before all subrogation and before reinsurance	30,846	8,351
Less:
Gross RMBS subrogation
Discount, RMBS subrogation
Subrogation recoveries
Less:
Gross other subrogation	(83)	(256)
Discount, other subrogation	22	77
Discounted other subrogation, before reinsurance	(61)	(179)
Gross claim liability, net of all subrogation and discounts, before reinsurance	30,785	8,172
Less: Unearned premium reserves	(1,987)	(5,126)
Plus: Loss adjustment expenses reserves
Claim liability reported on Balance Sheet, before reinsurance	28,798	3,046
Reinsurance recoverable reported on Balance Sheet		9
II [Member]
Summary of information related to policies currently included in Ambac's loss reserves
Number of policies	39	38
Remaining weighted-average contract period (in years)	18 years	17 years
Gross insured contractual payments outstanding:
Principal	2,025,972	2,060,102
Interest	1,136,858	1,088,036
Total	3,162,830	3,148,138
Gross undiscounted claim liability	55,755	52,355
Discount, gross claim liability	(3,740)	(3,800)
Gross claim liability before all subrogation and before reinsurance	52,015	48,555
Less:
Gross RMBS subrogation
Discount, RMBS subrogation
Subrogation recoveries
Less:
Gross other subrogation	0
Discount, other subrogation	0
Discounted other subrogation, before reinsurance	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	52,015	48,555
Less: Unearned premium reserves	(23,501)	(22,111)
Plus: Loss adjustment expenses reserves
Claim liability reported on Balance Sheet, before reinsurance	28,514	26,444
Reinsurance recoverable reported on Balance Sheet	6,240	5,714
III [Member]
Summary of information related to policies currently included in Ambac's loss reserves
Number of policies	122	125
Remaining weighted-average contract period (in years)	18 years	19 years
Gross insured contractual payments outstanding:
Principal	10,755,291	13,342,814
Interest	6,355,180	8,117,496
Total	17,110,471	21,460,310
Gross undiscounted claim liability	4,261,839	4,766,815
Discount, gross claim liability	(1,227,473)	(1,440,704)
Gross claim liability before all subrogation and before reinsurance	3,034,366	3,326,111
Less:
Gross RMBS subrogation	(203,515)	(461,725)
Discount, RMBS subrogation	2,995	12,278
Subrogation recoveries	(200,520)	(449,447)
Less:
Gross other subrogation	(51,912)	(52,871)
Discount, other subrogation	7,001	6,550
Discounted other subrogation, before reinsurance	(44,911)	(46,321)
Gross claim liability, net of all subrogation and discounts, before reinsurance	2,788,935	2,830,343
Less: Unearned premium reserves	(364,919)	(335,332)
Plus: Loss adjustment expenses reserves
Claim liability reported on Balance Sheet, before reinsurance	2,424,016	2,495,011
Reinsurance recoverable reported on Balance Sheet	143,202	139,499
IV [Member]
Summary of information related to policies currently included in Ambac's loss reserves
Number of policies	153	129
Remaining weighted-average contract period (in years)	10 years	9 years
Gross insured contractual payments outstanding:
Principal	13,190,115	13,092,057
Interest	3,459,207	3,587,812
Total	16,649,322	16,679,869
Gross undiscounted claim liability	8,837,054	7,632,709
Discount, gross claim liability	(807,445)	(828,061)
Gross claim liability before all subrogation and before reinsurance	8,029,609	6,804,648
Less:
Gross RMBS subrogation	(2,610,036)	(2,316,920)
Discount, RMBS subrogation	40,365	46,101
Subrogation recoveries	(2,569,671)	(2,270,819)
Less:
Gross other subrogation	(813,462)	(667,744)
Discount, other subrogation	26,373	45,912
Discounted other subrogation, before reinsurance	(787,089)	(621,832)
Gross claim liability, net of all subrogation and discounts, before reinsurance	4,672,849	3,911,997
Less: Unearned premium reserves	(146,339)	(158,687)
Plus: Loss adjustment expenses reserves	139,872	87,294
Claim liability reported on Balance Sheet, before reinsurance	4,666,382	3,840,604
Reinsurance recoverable reported on Balance Sheet	18,395	13,563
V [Member]
Summary of information related to policies currently included in Ambac's loss reserves
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	22	29
Total	69	76
Gross undiscounted claim liability	69	75
Discount, gross claim liability	(16)	(20)
Gross claim liability before all subrogation and before reinsurance	53	55
Less:
Gross RMBS subrogation
Discount, RMBS subrogation
Subrogation recoveries
Less:
Gross other subrogation
Discount, other subrogation
Discounted other subrogation, before reinsurance
Gross claim liability, net of all subrogation and discounts, before reinsurance	53	55
Less: Unearned premium reserves
Plus: Loss adjustment expenses reserves
Claim liability reported on Balance Sheet, before reinsurance	53	55
Reinsurance recoverable reported on Balance Sheet