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Insurance Regulations And Dividends (Narrative) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Insurance Regulations And Dividends [Line Items] |  |
Percentage of policyholders' surplus | 10.00% |
Percentage of adjusted net investment income | 100.00% |
Maximum percentage of notional asset swap | 5.00% |
Minimum [Member] |  |
Insurance Regulations And Dividends [Line Items] |  |
Policyholders' surplus | $ 65 |
MBIA Corp [Member] |  |
Insurance Regulations And Dividends [Line Items] |  |
Statutory net loss | 25 | $ 35
Statutory capital | 885 | 859
Policyholders' surplus | 609 |
Contingency reserves | $ 276 |
MBIA Corp [Member] | Minimum Surplus And Contingency Reserves [Member] |  |
Insurance Regulations And Dividends [Line Items] |  |
Investments in certain qualifing assets | 100.00% |
MBIA Corp [Member] | Loss Reserves And Unearned Premium Reserves [Member] |  |
Insurance Regulations And Dividends [Line Items] |  |
Investments in certain qualifing assets | 50.00% |
MBIA Corp [Member] | Policyholders Surplus [Member] |  |
Insurance Regulations And Dividends [Line Items] |  |
Statutory surplus negative impact | $ 75 |
Maximum percentage of statutory admitted assets invested in subsidiaries | 60.00% |
National [Member] |  |
Insurance Regulations And Dividends [Line Items] |  |
Dividends from subsidiaries | $ 114 | 220
Statutory capital | 3,400 | 3,300
Policyholders' surplus | 2,500 |
Contingency reserves | 910 |
Statutory net income | $ 284 | $ 238

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