The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the economic entity, including both controlling (parent) and noncontrolling interests. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, including any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

+ References+ Details

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

+ References+ Details

- Definition

Value of stock (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP), net of stock value of such awards forfeited. Stock issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

+ References+ Details

- Definition

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

+ References+ Details

Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Stockholders' Equity (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended																					12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Accumulated Deficit [Member]	Dec. 31, 2011 Accumulated Deficit [Member]	Dec. 31, 2012 Accumulated Other Comprehensive Income [Member]	Dec. 31, 2011 Accumulated Other Comprehensive Income [Member]	Dec. 31, 2011 Paid-in Capital [Member]	Dec. 31, 2012 Common Stock Held in Treasury, at Cost [Member]	Dec. 31, 2011 Common Stock Held in Treasury, at Cost [Member]	Dec. 31, 2012 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member]	Dec. 31, 2011 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member]	Dec. 31, 2012 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Accumulated Deficit [Member]	Dec. 31, 2011 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Accumulated Deficit [Member]	Dec. 31, 2012 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Accumulated Other Comprehensive Income [Member]	Dec. 31, 2011 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Accumulated Other Comprehensive Income [Member]	Dec. 31, 2012 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Preferred Stock [Member]	Dec. 31, 2011 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Preferred Stock [Member]	Dec. 31, 2010 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Preferred Stock [Member]	Dec. 31, 2012 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Common Stock [Member]	Dec. 31, 2011 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Common Stock [Member]	Dec. 31, 2010 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Common Stock [Member]	Dec. 31, 2011 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Paid-in Capital [Member]	Dec. 31, 2012 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Paid-in Capital [Member]	Dec. 31, 2012 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Common Stock Held in Treasury, at Cost [Member]	Dec. 31, 2011 AMBAC FINANCIAL GROUP, INC PARENT COMPANY ONLY [Member] Common Stock Held in Treasury, at Cost [Member]
Schedule Of Stockholders Equity [Line Items]
Beginning balance	$ (3,812,975)									$ (3,812,975)	$ (2,008,536)	$ (6,039,922)	$ (4,042,335)	$ 463,259	$ 291,774				$ 3,080	$ 3,080	$ 3,080	$ 2,187,485	$ 2,172,027	$ (411,419)	$ (448,540)
Total comprehensive loss	(97,434)	(1,788,839)	(256,678)	(1,960,431)	162,126	171,485				(94,552)	(1,788,946)	(256,678)	(1,960,431)	162,126	171,485
Stock-based compensation	(664)	(52,614)	(664)	(37,156)			(15,458)			(664)	(52,614)	(664)	(37,156)									(15,458)
Cost of shares acquired		(35)							(35)		(35)														(35)
Shares issued under equity plans	664	37,156						664	37,156	664	37,156													664	37,156
Ending balance	$ (3,907,527)	$ (3,812,975)								$ (3,907,527)	$ (3,812,975)	$ (6,297,264)	$ (6,039,922)	$ 625,385	$ 463,259				$ 3,080	$ 3,080	$ 3,080	$ 2,172,027	$ 2,172,027	$ (410,755)	$ (411,419)