Financial Guarantee Insurance Contracts - Summary of Rollforward of RMBS Subrogation, by Estimation Approach (Parenthetical) (Detail) (Predecessor Ambac [Member], Adverse Samples [Member])	3 Months Ended
	Mar. 31, 2013 Transactions
Predecessor Ambac [Member] | Adverse Samples [Member]
Summary Of Rollforward Of Subrogation By Estimation Approach [Line Items]
Number Of Transactions Added To Adverse Sample Population	2