Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statement of Total Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended								4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Apr. 30, 2013	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Successor [Member]
Revenues:
Other income										$ 4,364	$ 7,150	$ 12,498
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net										(46,764)	(25,659)	(25,794)
Net realized investment gains										(4,467)	(53,476)	(58,777)
Total revenues before expenses and reorganization items										581,048	644,658	328,670
Expenses:
Reorganization items	$ 0	$ 0	$ 0	$ 0	$ 0	$ 2	$ 186	$ 23		493	0	211
Income (loss) before income taxes and equity in undistributed net loss of subsidiaries	$ 395,576	$ (388,193)	$ 286,095	$ 216,580	$ 459,594	$ 84,773	$ (210,412)	$ 159,298		512,316	510,058	493,253
Income tax expense (benefit)										(7,514)	(17,364)	(9,557)
Net income (loss)										504,802	492,694	483,696
Other comprehensive income, after tax:
Net income (loss)										504,802	492,694	483,696
Unrealized gains (losses) on securities, net of deferred income taxes of $0										(41,910)	(159,730)	252,603
Gains (losses) on foreign currency translation, net of deferred income taxes of $0										43,165	(45,025)	(43,599)
Total other comprehensive income										12,102	(205,442)	208,188
Total comprehensive income attributable to Ambac Financial Group, Inc.										516,880	288,335	692,693
Predecessor [Member]
Revenues:
Other income									$ 8,363
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net									(467)
Net realized investment gains									(53,305)
Total revenues before expenses and reorganization items									640,388
Expenses:
Reorganization items									(2,745,180)
Income (loss) before income taxes and equity in undistributed net loss of subsidiaries									3,348,033
Income tax expense (benefit)									(755)
Net income (loss)									3,347,278
Other comprehensive income, after tax:
Net income (loss)									3,347,278
Unrealized gains (losses) on securities, net of deferred income taxes of $0									175,347
Gains (losses) on foreign currency translation, net of deferred income taxes of $0									(428)
Total other comprehensive income									175,104
Total comprehensive income attributable to Ambac Financial Group, Inc.									3,523,924
Ambac Financial Group, Inc Parent Company Only [Member] | Successor [Member]
Revenues:
Interest income										22,227	9,826	25,147
Other income										197,122	0	0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net											(155)
Net realized investment gains										(2)	27	46
Total revenues before expenses and reorganization items										219,351	9,644	25,101
Expenses:
Operating expenses										3,018	8,922	6,458
Total expenses										3,018	8,922	6,458
Income (loss) before income taxes, reorganization costs and equity in undistributed net loss of subsidiaries										216,333	722	18,643
Reorganization items										493	0	211
Income (loss) before income taxes and equity in undistributed net loss of subsidiaries										215,840	722	18,432
Income tax expense (benefit)										0	70,811	(221)
Income before equity in undistributed net income of subsidiaries										215,840	71,533	18,211
Equity in undistributed net income (loss) of subsidiaries										289,379	421,870	465,860
Net income (loss)										505,219	493,403	484,071
Other comprehensive income, after tax:
Net income (loss)										505,219	493,403	484,071
Unrealized gains (losses) on securities, net of deferred income taxes of $0										(41,910)	(159,730)	252,603
Gains (losses) on foreign currency translation, net of deferred income taxes of $0										42,724	(44,651)	(43,165)
Changes to postretirement benefit, net of tax										10,847	(687)	(816)
Total other comprehensive income										11,661	(205,068)	208,622
Total comprehensive income attributable to Ambac Financial Group, Inc.										$ 516,880	$ 288,335	$ 692,693
Ambac Financial Group, Inc Parent Company Only [Member] | Predecessor [Member]
Revenues:
Interest income									39
Other income									0
Net realized investment gains									0
Total revenues before expenses and reorganization items									39
Expenses:
Operating expenses									539
Total expenses									539
Income (loss) before income taxes, reorganization costs and equity in undistributed net loss of subsidiaries									(500)
Reorganization items									(2,745,180)
Income (loss) before income taxes and equity in undistributed net loss of subsidiaries									2,744,680
Income tax expense (benefit)									703
Income before equity in undistributed net income of subsidiaries									2,745,383
Equity in undistributed net income (loss) of subsidiaries									603,666
Net income (loss)									3,349,049
Other comprehensive income, after tax:
Net income (loss)									3,349,049
Unrealized gains (losses) on securities, net of deferred income taxes of $0									175,347
Gains (losses) on foreign currency translation, net of deferred income taxes of $0									(657)
Changes to postretirement benefit, net of tax									185
Total other comprehensive income									174,875
Total comprehensive income attributable to Ambac Financial Group, Inc.									$ 3,523,924