Business Developments And Risks And Uncertainties (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition [Line Items]
Number of business segments	3
Amount released from escrow account, subsequent fiscal period	$ 115,000,000
Repurchase of senior notes	172,000,000
Aggregate claim amount on CDS contracts	7,000,000,000
CMBS Pools [Member]
Business Acquisition [Line Items]
Insurance par exposure	15,600,000,000
ABS CDO [Member]
Business Acquisition [Line Items]
Insurance par exposure	4,300,000,000
MBIA Inc. [Member]
Business Acquisition [Line Items]
Liquid assets	239,000,000	386,000,000
MBIA Corp. [Member]
Business Acquisition [Line Items]
Liquid assets	345,000,000	534,000,000
Claims payments	1,200,000,000
Commuted gross insured exposure	$ 13,400,000,000