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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
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ (9) |  | $ 17
Other net realized gains (losses) |  | (1) |  | 3
Non Variable Interest Entity [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | (9) |  | 17
Other net realized gains (losses) |  | (1) |  | 3
Variable Interest Entity [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 4 |  | (33)
Other net realized gains (losses) |  | 0 |  | 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] | 0 |  | 6
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] | (2) |  | 3
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) |  | (8)
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] | (21) |  | (72)
Other 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] | 11 |  | 3
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] | (6) | [1] | (3)
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] | 27 |  | 45
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 | [3] |  |  | (45)
Other Liabilities [Member] | Non Variable Interest Entity [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Other net realized gains (losses) | [4] | $ (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 amount of a loss of $(45) million to a gain of $45 million.
[4] | Reported within "Other net realized gains (losses)" on MBIA's consolidated statements of operations.

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