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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, 2015 | Sep. 30, 2014 | Sep. 30, 2015 | Sep. 30, 2014
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ (55) |  | $ 57 |  | $ 20 | $ 63 |
Non Variable Interest Entity [Member] |  |  |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | (55) |  | 57 |  | 20 | 63 |
Variable Interest Entity [Member] |  |  |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 13 |  | 8 |  | 9 | 34 |
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] | 6 |  | 1 |  | 15 | 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] | 0 | [2] | (1) | 2 | [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 | [1] | (20) |  | (3) |  | (93) | (71) |
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] | (74) |  | (45) |  | (187) | (118) |
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] |  |  | (2) |  |  | (2) |
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] | (3) |  | 15 |  | 27 | 1 |
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] | $ 122 |  | $ 87 |  | $ 283 | $ 256 |
[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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