Fair Value Measurements - Information about Valuation Inputs for Variable Interest Entity Assets and Liabilities Classified as Level 3 (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	4 Months Ended		4 Months Ended		4 Months Ended		4 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended				3 Months Ended		5 Months Ended	9 Months Ended				3 Months Ended		5 Months Ended	9 Months Ended				3 Months Ended		5 Months Ended	9 Months Ended				4 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended				4 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended				4 Months Ended		3 Months Ended		5 Months Ended	9 Months Ended
	Sep. 30, 2014 Successor Ambac [Member] European ABS Transactions [Member]	Dec. 31, 2013 Successor Ambac [Member] European ABS Transactions [Member]	Sep. 30, 2014 Successor Ambac [Member] US Commercial ABS Transaction [Member]	Dec. 31, 2013 Successor Ambac [Member] US Commercial ABS Transaction [Member]	Apr. 30, 2013 Fair Value, Inputs, Level 3 [Member] Predecessor [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Predecessor [Member]	Apr. 30, 2013 Fair Value, Inputs, Level 3 [Member] Predecessor [Member] Investments [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Predecessor [Member] Investments [Member]	Apr. 30, 2013 Fair Value, Inputs, Level 3 [Member] Predecessor [Member] Other Assets [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Predecessor [Member] Other Assets [Member]	Apr. 30, 2013 Fair Value, Inputs, Level 3 [Member] Predecessor [Member] Derivative Financial Instruments, Liabilities [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 3 [Member] Predecessor [Member] Derivative Financial Instruments, Liabilities [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Jun. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Dec. 31, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Investments [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Investments [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Investments [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Investments [Member]	Jun. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Investments [Member]	Dec. 31, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Investments [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Investments [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Other Assets [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Other Assets [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Other Assets [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Other Assets [Member]	Jun. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Other Assets [Member]	Dec. 31, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Other Assets [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Other Assets [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Derivative Financial Instruments, Liabilities [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Derivative Financial Instruments, Liabilities [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Derivative Financial Instruments, Liabilities [Member]	Sep. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Derivative Financial Instruments, Liabilities [Member]	Jun. 30, 2014 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Derivative Financial Instruments, Liabilities [Member]	Dec. 31, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Derivative Financial Instruments, Liabilities [Member]	Jun. 30, 2013 Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member] Derivative Financial Instruments, Liabilities [Member]	Apr. 30, 2013 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Predecessor [Member]	Dec. 31, 2012 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Predecessor [Member]	Sep. 30, 2014 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2013 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2013 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2014 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Jun. 30, 2014 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Dec. 31, 2013 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Jun. 30, 2013 Loan Origination Commitments [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Apr. 30, 2013 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Predecessor [Member]	Dec. 31, 2012 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Predecessor [Member]	Sep. 30, 2014 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2013 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2013 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2014 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Jun. 30, 2014 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Dec. 31, 2013 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Jun. 30, 2013 Long-term Debt [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Apr. 30, 2013 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Predecessor [Member]	Dec. 31, 2012 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Predecessor [Member]	Sep. 30, 2014 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2013 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2013 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Sep. 30, 2014 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Jun. 30, 2014 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Dec. 31, 2013 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]	Jun. 30, 2013 Investment Contracts [Member] Fair Value, Inputs, Level 3 [Member] Successor Ambac [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability					$ 15,170,359	$ 14,416,488	$ 69,412	$ 60,402	$ 14,061	$ 14,557	$ (415,360)	$ (322,337)	$ 13,725,623	$ 15,341,277	$ 15,341,277	$ 13,725,623	$ 14,917,043	$ 14,253,705	$ 14,231,973	$ 62,660	$ 71,071	$ 71,071	$ 62,660	$ 66,352	$ 67,783	$ 68,572	$ 12,401	$ 13,671	$ 13,671	$ 12,401	$ 12,782	$ 13,384	$ 13,884	$ (215,902)	$ (305,674)	$ (305,674)	$ (215,902)	$ (218,661)	$ (186,934)	$ (340,663)	$ 14,752,053	$ 15,359,073	$ 12,503,484	$ 14,762,446	$ 14,762,446	$ 12,503,484	$ 13,743,231	$ 13,398,895	$ 13,820,878	$ (1,750,372)	$ (2,956,501)	$ (1,288,703)	$ (1,624,151)	$ (1,624,151)	$ (1,288,703)	$ (1,375,049)	$ (1,514,605)	$ (1,573,687)	$ 2,500,565	$ 2,261,294	$ 2,651,683	$ 2,423,914	$ 2,423,914	$ 2,651,683	$ 2,688,388	$ 2,475,182	$ 2,242,989
Coupon rate	0.33%	0.72%	5.88%	6.11%
Maturity	21 years 5 months 23 days	17 years 9 months 40 days	15 years 10 months 18 days	6 years 9 months 28 days
Yield	9.42%	8.02%	7.36%	11.95%
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Additions Of Consolidated Vies					(409,300)																																													(409,300)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Earnings					(1,057,181)		33		496		88,546		(301,522)	(291,195)	429,751	(666,194)				(835)	(467)	(863)	(1,676)				381	213	390	983				(3,885)	(37,126)	(107,253)	36,323				(956,402)		(209,028)	(195,305)	391,336	(735,597)				138,914		16,961	(21,816)	(26,163)	268,951				(328,768)		(105,116)	(36,694)	172,304	(235,178)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Gain Loss Included In Other Comprehensive Income Loss					776,014		(12,329)						758,705	(916,364)	(613,641)	305,933				254	(5,951)	(6,013)	595						0							0					849,833		678,944	(842,715)	(560,294)	270,727				(150,987)		(62,314)	76,533	48,319	(24,066)				89,497		141,821	(144,231)	(95,653)	58,677
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Purchases															0	(70,000)						0							0							0									0	(70,000)								0									0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Issues															0							0							0							0								0	0									0									0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Sales													(3,388)		0	(3,388)				(3,388)		0	(3,388)					0	0							0									0									0									0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Settlements					(716,488)		(3,286)				(4,477)		(70,951)	(102,781)	157,369	(294,849)				(885)	(4,192)	5,490	(2,608)						0					(1,126)	(2,137)	(2,433)	7,355				(713,589)		(73,042)	(96,452)	158,565	(733,492)				4,864		4,102	0	(4,253)	433,896								0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Into Level Three					0								0	4,526	(220,649)	0				0	273	273	0						0							0								0	0					0			4,253	(220,922)									0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Or Liability Transfers Out Of Level Three					1,598,492								(659,898)		(365,046)	(660,106)						0	(208)						0							0							(696,789)		0	(696,789)				1,598,492		36,891		(365,046)	36,891								0
Fair Value Asset Or Liability Measured On Recurring Basis Change In Unrealized Gains Losses Still Held					$ 1,053,758				$ (496)		$ (92,002)		$ 307,213	$ 286,586	$ (472,358)	$ 666,198					$ 0	$ 0					$ (381)	$ (213)	$ (390)	$ (983)				$ 3,229	$ 32,984	$ 65,509	$ (39,830)				$ 956,402		$ 215,296	$ 195,305	$ (391,336)	$ 736,732				$ (138,914)		$ (16,047)	$ 21,816	$ 26,163	$ (264,899)				$ 328,768		$ 105,116	$ 36,694	$ (172,304)	$ 235,178