Derivative Instruments - Summary of Notional Amounts of AFS's Trading Derivative Products (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$ 1,958,926	$ 2,776,103
Successor Ambac [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	1,958,926	2,776,103
AFS [Member] | Successor Ambac [Member] | Interest Rate Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	686,558	697,837
AFS [Member] | Successor Ambac [Member] | Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	1,484,081	1,540,976
AFS [Member] | Successor Ambac [Member] | Interest Rate Swaps-Basis Swaps [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	55,800	146,705
AFS [Member] | Successor Ambac [Member] | Futures Contracts [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	100,000	100,000
AFS [Member] | Successor Ambac [Member] | Other Contracts [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Derivative products, Notional Amount	$ 75,650	$ 75,650