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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, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | $ 21 | $ 25 | $ 20 | $ 51
Non Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | 21 | 25 | 20 | 51
Variable Interest Entity [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange |  | (23) | (36) | (47) | (16)
Investments Carried At Fair Value [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | [1] | (2) | (7) | 1 | (33)
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] | 0 | (1) | (4) | (4)
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 | [3] | (7) | 13 | (10) | 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 | 0 | 3 | 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 | [1] | 3 | 8 | 2 | 29
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] | $ (15) | $ (35) | $ (48) | $ (12)
[1] | Reported within "Net gains (losses) on financial instruments at fair value and foreign exchange" on MBIA's consolidated statements of operations.
[2] | Reported within "Net gains (losses) on financial instruments at fair value and foreign exchange-VIE" and "Other net realized gains (losses)-VIE" on MBIA's consolidated statements of operations.
[3] | Reported within "Net gains (losses) on financial instruments at fair value and foreign exchange-VIE" on MBIA's consolidated statements of operations.

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