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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, 2019 | Mar. 31, 2018
Accounts Notes And Loans Receivable [Line Items] |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ 22 | $ (9)
Other net realized gains (losses) |  | 1 | (1)
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 | (9)
Other net realized gains (losses) |  | 1 | (1)
Variable Interest Entity [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 18 | 4
Other net realized gains (losses) |  | (42) | 0
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 | [1] | 6 | (2)
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 | [2] | 26 | (6)
Loans Receivable and Other Instruments at Fair Value [Member] | Variable Interest Entity [Member] | Residential Mortgage Loans [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [2] | 34 | (21)
Loans Receivable and Other Instruments at Fair Value [Member] | Variable Interest Entity [Member] | Corporate Loans and Other Instruments [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [2] | 0 | 11
Loan Repurchase Commitments [Member] | 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 | 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 | [1] | (7) | (6)
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 | [2] | 84 | 27
Other Liabilities [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 | [3] | $ (1) | $ (2)
[1] | Reported within "Net gains (losses) of financial instruments at fair value and foreign exchange" on MBIA's consolidated statements of operations.
[2] | Reported within "Net gains (losses) of financial instruments at fair value and foreign exchange-VIE" on MBIA's consolidated statements of operations.
[3] | Reported within "Other net realized gains (losses)" on MBIA's consolidated statements of operations.

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