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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, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ 22 | $ (61) |  | $ 13 | $ (44) |
Other net realized gains (losses) |  | 0 | 34 |  | (1) | 37 |
Non Variable Interest Entity [Member] |  |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 22 | (61) |  | 13 | (44) |
Other net realized gains (losses) |  | 0 | 34 |  | (1) | 37 |
Variable Interest Entity [Member] |  |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 13 | 14 |  | 17 | (19) |
Other net realized gains (losses) |  | (93) | 0 |  | (93) | 28 |
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] | 9 | (2) |  | 9 | 4 |
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 |  | (5) | 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] | (6) | (5) |  | (12) | (14) |
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] | (54) | (30) |  | (76) | (102) |
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] | 0 | 4 |  | 11 | 7 |
Other Assets [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] | 0 | 0 |  | 0 | 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] | 12 | (19) |  | 6 | (22) |
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] | 56 | 45 | [3] | 83 | 90 | [3]
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member] | Previously reported [Member] |  |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  |  | (45) |  |  | (90) |
Other Liabilities [Member] | Non Variable Interest Entity [Member] |  |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |  |
Other net realized gains (losses) | [4] | $ 0 | $ 0 |  | $ (2) | $ 0 |
[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.
[3] | The Company revised its previously reported losses for the three months and six months ended June 30, 2017 of $(45) million and $(90) million, respectively, to gains of $45 million and $90 million, respectively.
[4] | Reported within "Other net realized gains (losses)" on MBIA's consolidated statements of operations.

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