Consolidated Statements of Total Comprehensive Income (USD $) In Thousands, except Per Share data, 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
Successor [Member]
Revenues:
Net premiums earned	$ 213,518	$ 246,360
Net investment income:
Securities available-for-sale and short-term	142,866	292,838
Other investments	3,580	8,108
Total net investment income	146,446	300,946
Other-than-temporary impairment losses:
Total other-than-temporary impairment losses	(47,418)	(26,632)
Portion of other -than-temporary impairment recognized in other comprehensive income	654	838
Net other-than-temporary impairments	(46,764)	(25,794)
Net realized investment gains	4,467	58,777
Change in fair value of credit derivatives:
Realized gains and other settlements	9,778	3,043
Unrealized gains (losses)	183,091	20,863
Net change in fair value of credit derivatives	192,869	23,906
Derivative products	114,771	(181,087)
Net realized losses on extinguishment of debt	0	(74,724)
Other income	4,364	12,498
Income (loss) on variable interest entities	(48,623)	(32,212)
Total revenues before expenses and reorganization items	581,048	328,670
Expenses:
Losses and loss expenses (benefit)	(185,138)	(545,574)
Insurance intangible amortization	99,658	151,830
Underwriting and operating expenses	68,769	101,474
Interest expense	84,950	127,476
Total expenses before reorganization items	68,239	(164,794)
Pre-tax (loss) income from continuing operations before reorganization items	512,809	493,464
Reorganization items	493	211
Pre-tax (loss) income from continuing operations	512,316	493,253
Provision for income taxes	7,514	9,557
Net income (loss)	504,802	483,696
Less: net (gain) loss attributable to noncontrolling interest	(417)	(375)
Net income (loss) attributable to common shareholders	505,219	484,071
Other comprehensive income (loss), after tax:
Net income (loss)	504,802	483,696
Unrealized gains (losses) on securities, net of deferred income taxes of $0	(41,910)	252,603
Gains (losses) on foreign currency translation, net of deferred income taxes of $0	43,165	(43,599)
Changes to postretirement benefit, net of tax of $0	10,847	(816)
Total other comprehensive income, net of tax	12,102	208,188
Total comprehensive income (loss)	516,904	691,884
Less: comprehensive (loss) gain attributable to the noncontrolling interest:
Net (gain) loss	(417)	(375)
Currency translation adjustments	441	(434)
Total comprehensive income (loss) attributable to Ambac Financial Group, Inc.	516,880	692,693
Net income (loss) per share attributable to Ambac Financial Group, Inc. common shareholders	$ 11.23	$ 10.73
Net income (loss) per diluted share attributable to Ambac Financial Group, Inc. common shareholders	$ 10.91	$ 10.31
Predecessor [Member]
Revenues:
Net premiums earned			130,000	414,604
Net investment income:
Securities available-for-sale and short-term			116,371	382,902
Other investments			369	0
Total net investment income			116,740	382,902
Other-than-temporary impairment losses:
Total other-than-temporary impairment losses			(467)	(15,659)
Portion of other -than-temporary impairment recognized in other comprehensive income			0	9,669
Net other-than-temporary impairments			(467)	(5,990)
Net realized investment gains			53,305	72,101
Change in fair value of credit derivatives:
Realized gains and other settlements			3,444	13,713
Unrealized gains (losses)			(63,828)	(22,932)
Net change in fair value of credit derivatives			(60,384)	(9,219)
Derivative products			(33,735)	(125,004)
Net realized losses on extinguishment of debt			0	(177,580)
Other income			8,363	106,098
Income (loss) on variable interest entities			426,566	27,777
Total revenues before expenses and reorganization items			640,388	685,689
Expenses:
Losses and loss expenses (benefit)			(38,056)	683,630
Insurance intangible amortization			0	0
Underwriting and operating expenses			44,566	139,029
Interest expense			31,025	112,320
Total expenses before reorganization items			37,535	934,979
Pre-tax (loss) income from continuing operations before reorganization items			602,853	(249,290)
Reorganization items			(2,745,180)	7,215
Pre-tax (loss) income from continuing operations			3,348,033	(256,505)
Provision for income taxes			755	2,849
Net income (loss)			3,347,278	(259,354)
Less: net (gain) loss attributable to noncontrolling interest			(1,771)	(2,676)
Net income (loss) attributable to common shareholders			3,349,049	(256,678)
Other comprehensive income (loss), after tax:
Net income (loss)			3,347,278	(259,354)
Unrealized gains (losses) on securities, net of deferred income taxes of $0			175,347	166,252
Gains (losses) on foreign currency translation, net of deferred income taxes of $0			(428)	(540)
Changes to postretirement benefit, net of tax of $0			185	(3,792)
Total other comprehensive income, net of tax			175,104	161,920
Total comprehensive income (loss)			3,522,382	(97,434)
Less: comprehensive (loss) gain attributable to the noncontrolling interest:
Net (gain) loss			(1,771)	(2,676)
Currency translation adjustments			229	(206)
Total comprehensive income (loss) attributable to Ambac Financial Group, Inc.			$ 3,523,924	$ (94,552)
Net income (loss) per share attributable to Ambac Financial Group, Inc. common shareholders			$ 11.07	$ (0.85)
Net income (loss) per diluted share attributable to Ambac Financial Group, Inc. common shareholders			$ 11.07	$ (0.85)