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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ (17) | $ (24) | $ 84
Other net realized gains (losses) |  | 0 | 31 | (282)
Non Variable Interest Entity [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | (17) | (24) | 84
Other net realized gains (losses) |  | 0 | 31 | (282)
Variable Interest Entity [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 25 | 130 | 0
Other net realized gains (losses) |  | (171) | 28 | 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] | (11) | 8 | 7
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] | (25) | (22) | (124)
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] | (100) | (158) | (268)
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] | 11 | 52 | 0
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] | 12 | 3 | 8
Other Assets [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] | 0 | (3) | 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] | 19 | (14) | 4
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] | 118 | 230 | 383
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] | $ (2) | $ 0 | $ 0
[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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