Business Developments And Risks And Uncertainties (Narrative) (Detail) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended		1 Months Ended			1 Months Ended							3 Months Ended		3 Months Ended
	Mar. 31, 2013 Segment	May 06, 2013	May 07, 2013 Subsequent Event [Member] Plaintiff	Mar. 31, 2013 Amount Outstanding [Member]	May 06, 2013 Amount Outstanding before Bofa Settlement [Member] Subsequent Event [Member]	May 06, 2013 Flagstar Settlement [Member] Subsequent Event [Member]	May 06, 2013 Bank of America [Member] Subsequent Event [Member]	May 06, 2013 Bank of America [Member] Insured Credit Default Swaps [Member] Subsequent Event [Member]	May 06, 2013 Bank of America [Member] Warrants [Member] Subsequent Event [Member]	May 06, 2013 Bank of America [Member] Cash [Member] Subsequent Event [Member]	May 06, 2013 Bank of America [Member] Corporate Obligations [Member] Subsequent Event [Member]	May 07, 2013 Societe Generale [Member] Subsequent Event [Member]	Mar. 31, 2013 MBIA Corp. [Member]	Dec. 31, 2012 MBIA Corp. [Member]	Mar. 31, 2013 MBIA Corp. [Member] Subsequent Event [Member]	Mar. 31, 2013 MBIA Inc. [Member]	Dec. 31, 2012 MBIA Inc. [Member]	Mar. 31, 2013 CMBS Pools [Member] MBIA Corp. [Member]	Mar. 31, 2013 ABS CDO [Member] MBIA Corp. [Member]
Business Acquisition [Line Items]
Number of business segments	3
Amount received on litigation settlement						$ 110,000,000	$ 1,700,000,000			$ 1,600,000,000	$ 136,000,000
Debt instrument, interest percentage		5.70%
Commuted gross insured exposure							7,400,000,000	6,100,000,000				4,200,000,000	2,100,000,000		13,400,000,000
Warrant term							5 years
Warrant to purchase of common stock, shares									9.94
Warrant to purchase of common stock, share price							9.59
Settlement without prejudice term							1 year
Secured revolving credit agreement							500,000,000
Secured revolving credit agreement term							3 years
Subsidiary collateral percentage							65.00%
Minimum statutory capital requirement							750,000,000
National secured loan				1,700,000,000	1,600,000,000
Liquid assets													258,000,000	345,000,000		373,000,000	239,000,000
Amount released from escrow account	115,000,000
Claims payments													139,000,000
Number of resolved Article 78 plaintiffs			18
Insurance par exposure																		$ 17,600,000,000	$ 4,100,000,000