Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Cash Flows (Detail) (USD $)	8 Months Ended	12 Months Ended	4 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014	Apr. 30, 2013	Dec. 31, 2012
Condensed Cash Flow Statements, Captions [Line Items]
Junior Surplus Notes To Be Issued			$ 350,000,000
Successor [Member]
Cash flows from operating activities:
Net income (loss)	504,802,000	483,696,000
Adjustments to reconcile net income loss to net cash used in operating activities:
Reorganization items	493,000	211,000
Net realized investment gains	(4,467,000)	(58,777,000)
Decrease in current income taxes payable	5,148,000	4,963,000
Share-based compensation	1,106,000	3,450,000
Investment income due and accrued	298,000	12,648,000
Other, net	(137,150,000)	152,846,000
Net cash (used in) provided by operating activities	186,908,000	(971,509,000)
Cash flows from investing activities:
Proceeds from matured bonds	613,345,000	1,402,904,000
Purchases of bonds	(2,213,116,000)	(2,937,782,000)
Change in short-term investments	455,495,000	(88,946,000)
Net cash provided by (used in) investing activities	(247,510,000)	1,275,153,000
Proceeds from the sale of Junior Surplus Notes of the Segregated Account	0	224,262,000
Cash flows from financing activities:
Proceeds from warrant exercise	16,000	16,000
Net cash (used in) financing activities	(14,979,000)	(307,111,000)
Net cash flow	(75,581,000)	(3,467,000)
Cash and cash equivalents end of period	152,951,000	77,370,000
Cash at end of period	77,370,000	73,903,000
Cash paid during the period for:
Income taxes	1,656,000	4,400,000
Professional fees paid for services rendered in connection with the Chapter 11 proceeding	15,546,000	272,000
Predecessor [Member]
Cash flows from operating activities:
Net income (loss)			3,347,278,000	(259,354,000)
Adjustments to reconcile net income loss to net cash used in operating activities:
Reorganization items			(2,745,180,000)	7,215,000
Net realized investment gains			(53,305,000)	(72,101,000)
Decrease in current income taxes payable			(101,188,000)	1,069,000
Share-based compensation			0	0
Investment income due and accrued			1,781,000	5,586,000
Other, net			62,122,000	105,906,000
Net cash (used in) provided by operating activities			(683,000)	(613,898,000)
Cash flows from investing activities:
Proceeds from matured bonds			307,472,000	1,109,468,000
Purchases of bonds			(286,633,000)	(798,740,000)
Change in short-term investments			(64,956,000)	121,413,000
Net cash provided by (used in) investing activities			115,316,000	1,037,980,000
Proceeds from the sale of Junior Surplus Notes of the Segregated Account			0	0
Cash flows from financing activities:
Proceeds from warrant exercise			0	0
Net cash (used in) financing activities			(5,519,000)	(396,244,000)
Net cash flow			109,114,000	27,838,000
Cash and cash equivalents end of period			43,837,000	15,999,000
Cash at end of period			152,951,000	43,837,000
Cash paid during the period for:
Income taxes			102,129,000	1,493,000
Professional fees paid for services rendered in connection with the Chapter 11 proceeding			3,860,000	9,141,000
Ambac Financial Group, Inc Parent Company Only [Member] | Successor [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Junior Surplus Notes To Be Issued	167,020,000	0
Cash flows from operating activities:
Net income (loss)	505,219,000	484,071,000
Adjustments to reconcile net income loss to net cash used in operating activities:
Equity in undistributed net (income) loss of non-debtor subsidiaries	(289,379,000)	(465,860,000)
Reorganization items	493,000	211,000
Net realized investment gains	(2,000)	46,000
Decrease in current income taxes payable	0	221,000
Share-based compensation	1,106,000	3,450,000
Investment income due and accrued	(11,942,000)	11,905,000
Decrease in other assets	(1,677,000)	(834,000)
Other, net	(28,030,000)	(36,624,000)
Net cash (used in) provided by operating activities	8,768,000	(3,414,000)
Cash flows from investing activities:
Proceeds from matured bonds	14,355,000	65,032,000
Purchases of bonds	(42,506,000)	(271,181,000)
Change in short-term investments	19,360,000	(14,617,000)
Net cash provided by (used in) investing activities	(8,791,000)	(220,766,000)
Proceeds from the sale of Junior Surplus Notes of the Segregated Account	0	224,262,000
Cash flows from financing activities:
Proceeds from warrant exercise	16,000	16,000
Net cash (used in) financing activities	16,000	224,278,000
Net cash flow	(7,000)	98,000
Cash and cash equivalents end of period	50,000	43,000
Cash at end of period	43,000	141,000
Cash paid during the period for:
Income taxes	0	0
Professional fees paid for services rendered in connection with the Chapter 11 proceeding	15,546,000	272,000
Ambac Financial Group, Inc Parent Company Only [Member] | Predecessor [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Junior Surplus Notes To Be Issued			0	0
Cash flows from operating activities:
Net income (loss)			3,349,049,000	(256,678,000)
Adjustments to reconcile net income loss to net cash used in operating activities:
Equity in undistributed net (income) loss of non-debtor subsidiaries			(603,666,000)	250,729,000
Reorganization items			(2,745,180,000)	7,215,000
Net realized investment gains			0	0
Decrease in current income taxes payable			(1,900,000)	0
Share-based compensation			0	0
Investment income due and accrued			(6,000)	9,000
Decrease in other assets			3,182,000	21,000
Other, net			(4,107,000)	(6,334,000)
Net cash (used in) provided by operating activities			(2,628,000)	(5,038,000)
Cash flows from investing activities:
Proceeds from matured bonds			0	0
Purchases of bonds			0	0
Change in short-term investments			2,637,000	4,583,000
Net cash provided by (used in) investing activities			2,637,000	4,583,000
Proceeds from the sale of Junior Surplus Notes of the Segregated Account			0	0
Cash flows from financing activities:
Proceeds from warrant exercise			0	0
Net cash (used in) financing activities			0	0
Net cash flow			9,000	(455,000)
Cash and cash equivalents end of period			41,000	496,000
Cash at end of period			50,000	41,000
Cash paid during the period for:
Income taxes			1,900,000	0
Professional fees paid for services rendered in connection with the Chapter 11 proceeding			$ 3,860,000	$ 9,141,000