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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 | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ (11) | $ 38 | $ (55) | $ (17)
Other net realized gains (losses) |  | (1) | (2) | 36 | (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 |  | (11) | 38 | (55) | (17)
Other net realized gains (losses) |  | (1) | (2) | 36 | (3)
Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 21 | 8 | 2 | 0
Other net realized gains (losses) |  | 0 | 0 | 28 | 0
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) | 3 | 3 | 8
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] | 2 | 2 | 8 | 8
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] | (2) | (12) | (16) | (109)
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 | [2] | (55) | (50) | (157) | (190)
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 | [2] | (2) |  | 4 |
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] | (4) | (2) | (26) | (2)
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] | 70 | $ 70 | 160 | $ 307
Other Liabilities [Member] | Non Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Other net realized gains (losses) | [3] | $ (1) |  | $ (1) |
[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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