Fair Value Measurements - Information about Valuation Inputs for Variable Interest Entity Assets and Liabilities Classified as Level 3 (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2013 Successor Ambac [Member] European ABS Transactions [Member]	Sep. 30, 2013 Successor Ambac [Member] US Commercial ABS Transaction [Member]	Dec. 31, 2012 Predecessor Ambac [Member] European ABS Transactions [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Coupon rate	0.72%	6.02%	1.64%
Maturity	18 years	5 years 7 months 24 days	12 years 4 months 2 days
Yield	1.12%	9.73%	4.02%