Insurance Regulations And Dividends (Details) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2010
Insurance Regulations And Dividends [Line Items]
Percentage of policyholders' surplus		10.00%
Adjusted net investment income		100.00%
Declared and paid a dividend		$ 0
Net loss		477,000,000	434,000,000
Qualifying asset shortfall	582,000,000	582,000,000
Contingency reserve release to surplus	582,000,000	900,000,000
National [Member]
Insurance Regulations And Dividends [Line Items]
Dividend capacity		142,000,000	91,000,000
Policyholders' surplus	1,400,000,000	1,400,000,000
Contingency reserves	1,400,000,000	1,400,000,000
Statutory net income		478,000,000	409,000,000
Statutory capital		2,800,000,000	2,400,000,000
MBIA Corp. [Member]
Insurance Regulations And Dividends [Line Items]
Policyholders' surplus	1,600,000,000	1,600,000,000
Contingency reserves	706,000,000	706,000,000
Statutory capital		$ 2,300,000,000	$ 2,700,000,000