Insurance Regulations And Dividends (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Insurance Regulations And Dividends [Line Items]
Percentage of policyholders' surplus	10.00%
Adjusted net investment income	100.00%
Option B [Member]
Insurance Regulations And Dividends [Line Items]
Deficit of qualifying assets	$ 140,000,000
Contingency reserve release to surplus	140,000,000
MBIA Corp. [Member]
Insurance Regulations And Dividends [Line Items]
Declared and paid a dividend	0	0
Aggregate risk limits	56,000,000
Net loss	843,000,000	477,000,000
Statutory capital	1,500,000,000	2,300,000,000
Policyholders' surplus	965,000,000
Contingency reserves	493,000,000
National [Member]
Insurance Regulations And Dividends [Line Items]
Dividend capacity	200,000,000	142,000,000
Unassigned surplus	0
Statutory capital	3,200,000,000	2,800,000,000
Policyholders' surplus	2,000,000,000
Contingency reserves	1,200,000,000
Statutory net income	$ 416,000,000	$ 478,000,000