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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 | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ (24) |  | $ 84 |  | $ 63
Other net realized gains (losses) |  | 31 |  | (282) |  | 17
Non Variable Interest Entity [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | (24) |  | 84 |  | 63
Other net realized gains (losses) |  | 31 |  | (282) |  | 17
Variable Interest Entity [Member] |  |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 130 |  | 0 |  | 42
Other net realized gains (losses) |  | 28 |  | 0 |  | 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 |  | 8 |  | 17
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] | 8 |  | 7 |  | (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] | (22) |  | (124) |  | (146)
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] | (158) |  | (268) |  | (246)
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] | 52 |  | 0 |  | 0
Other [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] | (3) |  | 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 |  | (14) | [2] | 4 | [2] | 36
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] | $ 230 |  | $ 383 |  | $ 381
[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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