Derivative Instruments - Summary of Location and Amount of Gains and Losses of Derivative Contracts (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	5 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended
	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member]	Sep. 30, 2013 Successor Ambac [Member] Variable Interest Entity [Member]	Sep. 30, 2013 Successor Ambac [Member] Variable Interest Entity [Member]	Sep. 30, 2013 Successor Ambac [Member] Financial Services Derivatives Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Financial Services Derivatives Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Credit Derivatives [Member] Financial Guarantee [Member] Net Change in Fair Value of Credit Derivatives [Member]	Sep. 30, 2013 Successor Ambac [Member] Credit Derivatives [Member] Financial Guarantee [Member] Net Change in Fair Value of Credit Derivatives [Member]	Sep. 30, 2013 Successor Ambac [Member] Interest Rate Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Sep. 30, 2013 Successor Ambac [Member] Interest Rate Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Sep. 30, 2013 Successor Ambac [Member] Interest Rate Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Interest Rate Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Currency Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Sep. 30, 2013 Successor Ambac [Member] Currency Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Sep. 30, 2013 Successor Ambac [Member] Currency Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Currency Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Futures Contracts [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Futures Contracts [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Other Derivatives [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Other Derivatives [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2013 Successor Ambac [Member] Call Options on Long-Term Debt [Member] Other Income [Member]	Sep. 30, 2013 Successor Ambac [Member] Call Options on Long-Term Debt [Member] Other Income [Member]	Sep. 30, 2012 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Sep. 30, 2012 Predecessor Ambac [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Variable Interest Entity [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Variable Interest Entity [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Variable Interest Entity [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Financial Services Derivatives Products [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Financial Services Derivatives Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Financial Services Derivatives Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Credit Derivatives [Member] Financial Guarantee [Member] Net Change in Fair Value of Credit Derivatives [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Credit Derivatives [Member] Financial Guarantee [Member] Net Change in Fair Value of Credit Derivatives [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Credit Derivatives [Member] Financial Guarantee [Member] Net Change in Fair Value of Credit Derivatives [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Interest Rate Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Interest Rate Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Interest Rate Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Interest Rate Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Interest Rate Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Interest Rate Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Currency Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Currency Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Currency Swaps [Member] Income on Variable Interest Entities [Member] Variable Interest Entity [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Currency Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Currency Swaps [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Futures Contracts [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Futures Contracts [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Futures Contracts [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Other Derivatives [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Other Derivatives [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Other Derivatives [Member] Financial Services Derivatives Products [Member] Derivative Products [Member]	Sep. 30, 2012 Predecessor Ambac [Member] Call Options on Long-Term Debt [Member] Other Income [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Derivative instruments, gain (loss) recognized in income, net, Total	$ (13,855)	$ 556,812	$ (57,421)	$ 378,313	$ 12,372	$ 96,085	$ 31,194	$ 82,414	$ (63,421)	$ 374,203	$ 13,299	$ 87,468	$ 6,000	$ 4,110			$ (961)	$ 8,870	$ 34	$ (253)			$ (5,709)	$ (297,855)	$ 26,473	$ 2,858	$ (203,736)	$ 26,101	$ (36,007)	$ (33,735)	$ (113,141)	$ 27,440	$ (60,384)	$ 12,803	$ (2,723)	$ (203,620)	$ 42,514	$ (33,036)	$ (30,622)	$ (99,026)	$ 5,581	$ (116)	$ (16,413)	$ 570	$ 807	$ (3,485)	$ (3,133)	$ (15,247)	$ (56)	$ 20	$ 325	$ 100,710