Insurance In Force (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Transactions guaranteed by MBIA on behalf of various investment management service affiliates	$ 3,400,000,000	$ 4,400,000,000
Amount available under these letters of credit and trust arrangements	8,000,000
Aggregate amount of insurance in force ceded to reinsurers	6,000,000,000	7,500,000,000
Aggregate amount of insured par outstanding ceded to reinsurers	3,420,000,000	4,300,000,000
Recoveries received on claims for financial guarantee policies under reinsurance contracts	4,000,000	10,000,000	21,000,000
Ceding commissions from reinsurance	3,000,000	3,000,000	7,000,000
Financial Guaranty Insurance Company [Member]
Third party reinsurance	4,400,000,000	9,100,000,000
Amount of insurance in force for FGIC policies	7,800,000,000	16,100,000,000
Guarantees Of Derivative Contracts [Member]
Maximum amount of future guarantee payments	51,900,000,000
Guarantees of derivative contracts, maturity range, minimum (Years)	1 year
Guarantees of derivative contracts, maturity range, maximum (Years)	70 years
Derivative liabilities	2,900,000,000	4,800,000,000
Investment Agreement Contracts and MTNs [Member]
Maximum amount of future guarantee payments	$ 3,400,000,000
Future guarantee payments, maturity range, minimum (years)	1 year
Future guarantee payments, maturity range, maximum (years)	33 years
Minimum [Member]
Insurance in force, expected maturity range, years	1
Maximum [Member]
Insurance in force, expected maturity range, years	45