Derivative Instruments - Summary of Notional Amounts of AFS's Trading Derivative Products (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013 Successor Ambac [Member] Interest Rate Swaps [Member]	Jun. 30, 2013 Successor Ambac [Member] Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]	Jun. 30, 2013 AFS [Member] Successor Ambac [Member] Interest Rate Swaps [Member]	Jun. 30, 2013 AFS [Member] Successor Ambac [Member] Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]	Jun. 30, 2013 AFS [Member] Successor Ambac [Member] Interest Rate Swaps-Basis Swaps [Member]	Jun. 30, 2013 AFS [Member] Successor Ambac [Member] Futures Contracts [Member]	Jun. 30, 2013 AFS [Member] Successor Ambac [Member] Other derivatives [Member]	Dec. 31, 2012 AFS [Member] Predecessor Ambac [Member] Interest Rate Swaps [Member]	Dec. 31, 2012 AFS [Member] Predecessor Ambac [Member] Interest Rate Swaps-Pay-Fixed/Receive-Variable [Member]	Dec. 31, 2012 AFS [Member] Predecessor Ambac [Member] Interest Rate Swaps-Basis Swaps [Member]	Dec. 31, 2012 AFS [Member] Predecessor Ambac [Member] Futures Contracts [Member]	Dec. 31, 2012 AFS [Member] Predecessor Ambac [Member] Other derivatives [Member]
Schedule Of Notional Amounts Of Parents Financial Services Trading Derivative Products [Line Items]
Derivative products, Notional Amount	$ 1,669,298	$ 4,356,549	$ 1,782,999	$ 4,707,454	$ 703,384	$ 1,571,088	$ 161,690	$ 100,000	$ 75,650	$ 727,926	$ 1,657,382	$ 161,690	$ 161,500	$ 75,651