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Insurance Regulations And Dividends (Detail) (USD $) | 12 Months Ended
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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

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