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Fair Value Of Financial Instruments (Gains And Losses On Fair Value Option Included In The Company's Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ (61) | $ 14 | $ (44) | $ (55)
Non Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | (61) | 14 | (44) | (55)
Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 14 | (7) | (19) | (8)
Variable Interest Entity [Member] | Loan Repurchase Commitments [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [1] | (2) | 2 | 4 | 5
Investments Carried At Fair Value [Member] | Non Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [2] | 3 | 3 | 6 | 6
Fixed Maturity Securities Held At Fair Value - VIE [Member] | Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [1] | (5) | (13) | (14) | (97)
Residential Mortgage Loans [Member] | Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [1] | (30) | (70) | (102) | (140)
Corporate Loans [Member] | Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [1] | 4 | 0 | 7 | 0
Medium Term Notes [Member] | Non Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [2] | (19) | 4 | (22) | 0
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [1] | $ (45) | $ 71 | $ (90) | $ 238
[1] | Reported within Net gains (losses) of financial instruments at fair value and foreign exchange-VIE on MBIA's consolidated statements of operations.
[2] | Reported within Net gains (losses) of financial instruments at fair value and foreign exchange on MBIA's consolidated statements of operations.

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