Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Stockholders' Equity (Detail) (USD $) In Thousands, unless otherwise specified	8 Months Ended	12 Months Ended	4 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014	Apr. 30, 2013	Dec. 31, 2012	May 01, 2013
Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 460,415	$ 978,422
Issuance of new equity in connection with emergence from Chapter 11					185,000
Total comprehensive income (loss)	516,904	691,884
Stock-based compensation	1,106	3,450
Cost of shares acquired		(37)
Warrants exercised	16	16
Cost of shares acquired	19
Ending balance	978,422	1,673,735
Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(3,246,967)	(3,149,533)
Total comprehensive income (loss)			3,522,382	(97,434)
Stock-based compensation			(60)	(664)
Cost of shares acquired			60	664
Elimination of Predecessor Ambac Shareholder equity accounts			0
Ending balance			275,415	(3,246,967)
Retained Earnings/Accumulated Deficit [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	505,219
Issuance of new equity in connection with emergence from Chapter 11					0
Total comprehensive income (loss)	505,219	484,071
Stock-based compensation	0	0
Cost of shares acquired		0
Warrants exercised	0	0
Cost of shares acquired	0
Ending balance	505,219	989,290
Retained Earnings/Accumulated Deficit [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(6,297,264)	(6,039,922)
Total comprehensive income (loss)			3,349,049	(256,678)
Stock-based compensation			(60)	(664)
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			(2,948,275)
Ending balance			0	(6,297,264)
Accumulated Other Comprehensive Income (Loss) [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	11,661
Issuance of new equity in connection with emergence from Chapter 11					0
Total comprehensive income (loss)	11,661	208,622
Stock-based compensation	0	0
Cost of shares acquired		0
Warrants exercised	0	0
Cost of shares acquired	0
Ending balance	11,661	220,283
Accumulated Other Comprehensive Income (Loss) [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			625,385	463,259
Total comprehensive income (loss)			174,875	162,126
Stock-based compensation			0	0
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			800,260
Ending balance			0	625,385
Preferred Stock [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	0
Issuance of new equity in connection with emergence from Chapter 11					0
Total comprehensive income (loss)	0	0
Stock-based compensation	0	0
Cost of shares acquired		0
Warrants exercised	0	0
Cost of shares acquired	0
Ending balance	0	0
Preferred Stock [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	0
Total comprehensive income (loss)			0	0
Stock-based compensation			0	0
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			0
Ending balance			0	0
Common Stock [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	450	450
Issuance of new equity in connection with emergence from Chapter 11					450
Total comprehensive income (loss)	0	0
Stock-based compensation	0	0
Cost of shares acquired		0
Warrants exercised	0	0
Cost of shares acquired	0
Ending balance	450	450
Common Stock [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			3,080	3,080
Total comprehensive income (loss)			0	0
Stock-based compensation			0	0
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			3,080
Ending balance			0	3,080
Additional Paid-in Capital [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	184,550	185,672
Issuance of new equity in connection with emergence from Chapter 11					184,550
Total comprehensive income (loss)	0	0
Stock-based compensation	1,106	3,450
Cost of shares acquired		0
Warrants exercised	16	16
Cost of shares acquired	0
Ending balance	185,672	189,138
Additional Paid-in Capital [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			2,172,027	2,172,027
Total comprehensive income (loss)			0	0
Stock-based compensation			0	0
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			2,172,027
Ending balance			0	2,172,027
Common Stock Held in Treasury, at Cost [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	(19)
Issuance of new equity in connection with emergence from Chapter 11					0
Total comprehensive income (loss)	0	0
Stock-based compensation	0	0
Cost of shares acquired		(37)
Warrants exercised	0	0
Cost of shares acquired	19
Ending balance	(19)	(56)
Common Stock Held in Treasury, at Cost [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(410,755)	(411,419)
Total comprehensive income (loss)			0	0
Stock-based compensation			0	0
Cost of shares acquired			60	664
Elimination of Predecessor Ambac Shareholder equity accounts			(410,695)
Ending balance			0	(410,755)
Ambac Financial Group, Inc Parent Company Only [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	185,000	702,983
Issuance of new equity in connection with emergence from Chapter 11					185,000
Total comprehensive income (loss)	516,880	692,693
Stock-based compensation	1,106	3,450
Cost of shares acquired		(37)
Warrants exercised	16	16
Cost of shares acquired	(19)
Ending balance	702,983	1,399,105
Ambac Financial Group, Inc Parent Company Only [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(3,907,527)	(3,812,975)
Total comprehensive income (loss)			3,523,924	(94,552)
Stock-based compensation			60	664
Cost of shares acquired			60	664
Elimination of Predecessor Ambac Shareholder equity accounts			383,603
Ending balance			0	(3,907,527)
Ambac Financial Group, Inc Parent Company Only [Member] | Retained Earnings/Accumulated Deficit [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	505,219
Issuance of new equity in connection with emergence from Chapter 11					0
Total comprehensive income (loss)	505,219	484,071
Stock-based compensation	0	0
Cost of shares acquired		0
Warrants exercised	0	0
Cost of shares acquired	0
Ending balance	505,219	989,290
Ambac Financial Group, Inc Parent Company Only [Member] | Retained Earnings/Accumulated Deficit [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(6,297,264)	(6,039,922)
Total comprehensive income (loss)			3,349,049	(256,678)
Stock-based compensation			60	664
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			2,948,275
Ending balance			0	(6,297,264)
Ambac Financial Group, Inc Parent Company Only [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	11,661
Issuance of new equity in connection with emergence from Chapter 11					0
Total comprehensive income (loss)	11,661	208,622
Stock-based compensation	0	0
Cost of shares acquired		0
Warrants exercised	0	0
Cost of shares acquired	0
Ending balance	11,661	220,283
Ambac Financial Group, Inc Parent Company Only [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			625,385	463,259
Total comprehensive income (loss)			174,875	162,126
Stock-based compensation			0	0
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			(800,260)
Ending balance			0	625,385
Ambac Financial Group, Inc Parent Company Only [Member] | Preferred Stock [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	0
Issuance of new equity in connection with emergence from Chapter 11					0
Total comprehensive income (loss)	0	0
Stock-based compensation	0	0
Cost of shares acquired		0
Warrants exercised	0	0
Cost of shares acquired	0
Ending balance	0	0
Ambac Financial Group, Inc Parent Company Only [Member] | Preferred Stock [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			0	0
Total comprehensive income (loss)			0	0
Stock-based compensation			0	0
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			0
Ending balance			0	0
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	450	450
Issuance of new equity in connection with emergence from Chapter 11					450
Total comprehensive income (loss)	0	0
Stock-based compensation	0	0
Cost of shares acquired		0
Warrants exercised	0	0
Cost of shares acquired	0
Ending balance	450	450
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			3,080	3,080
Total comprehensive income (loss)			0	0
Stock-based compensation			0	0
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			(3,080)
Ending balance			0	3,080
Ambac Financial Group, Inc Parent Company Only [Member] | Additional Paid-in Capital [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	184,550	185,672
Issuance of new equity in connection with emergence from Chapter 11					184,550
Total comprehensive income (loss)	0	0
Stock-based compensation	1,106	3,450
Cost of shares acquired		0
Warrants exercised	16	16
Cost of shares acquired	0
Ending balance	185,672	189,138
Ambac Financial Group, Inc Parent Company Only [Member] | Additional Paid-in Capital [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			2,172,027	2,172,027
Total comprehensive income (loss)			0	0
Stock-based compensation			0	0
Cost of shares acquired			0	0
Elimination of Predecessor Ambac Shareholder equity accounts			(2,172,027)
Ending balance			0	2,172,027
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock Held in Treasury, at Cost [Member] | Successor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	0	(19)
Issuance of new equity in connection with emergence from Chapter 11					0
Total comprehensive income (loss)	0	0
Stock-based compensation	0	0
Cost of shares acquired		(37)
Warrants exercised	0	0
Cost of shares acquired	(19)
Ending balance	(19)	(56)
Ambac Financial Group, Inc Parent Company Only [Member] | Common Stock Held in Treasury, at Cost [Member] | Predecessor [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			(410,755)	(411,419)
Total comprehensive income (loss)			0	0
Stock-based compensation			0	0
Cost of shares acquired			60	664
Elimination of Predecessor Ambac Shareholder equity accounts			410,695
Ending balance			$ 0	$ (410,755)