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Fair Value of Financial Instruments (Quantitative Information Regarding The Significant Unobservable Inputs For Certain Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
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Discounted Cash Flow [Member] | Equity Investments [Member] | EBITDA Multiples Discount Rate Hard Asset Values Type Certificate Values [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Fair Value, assets | [1] |  | $ 108
Discounted Cash Flow [Member] | Loans Carried at Fair Value [Member] | Discount Rate [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Fair Value, assets | [2] | $ 15 |
Discounted Cash Flow Type Certificate [Member] | Equity Investments [Member] | Discount Rate EBITDA Multiple EBITDA Royalty Share [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Fair Value, assets | [2] | 52 |
Variable Interest Entity Primary Beneficiary [Member] | Variable Interest Entity Notes [Member] | Impact Of Financial Guarantee [Member] | Market Prices Of VIE Assets Adjusted For Financial Guarantees Provided Or Market Prices Of Similar Liabilities [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Fair value, liabilities |  |  | 78
Variable Interest Entity Primary Beneficiary [Member] | Loans Receivable and Other Instruments at Fair Value [Member] | Impact Of Financial Guarantee [Member] | Market Prices of Similar Liabilities Adjusted for Financial Guarantees Provided to VIE Obligations [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Fair Value, assets |  | $ 28 | $ 35
Variable Interest Entity Primary Beneficiary [Member] | Minimum [Member] | Variable Interest Entity Notes [Member] | Impact Of Financial Guarantee [Member] | Market Prices Of VIE Assets Adjusted For Financial Guarantees Provided Or Market Prices Of Similar Liabilities [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  |  | 74.00%
Variable Interest Entity Primary Beneficiary [Member] | Minimum [Member] | Loans Receivable and Other Instruments at Fair Value [Member] | Impact Of Financial Guarantee [Member] | Market Prices of Similar Liabilities Adjusted for Financial Guarantees Provided to VIE Obligations [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  | 27.00% | 27.00%
Variable Interest Entity Primary Beneficiary [Member] | Maximum [Member] | Variable Interest Entity Notes [Member] | Impact Of Financial Guarantee [Member] | Market Prices Of VIE Assets Adjusted For Financial Guarantees Provided Or Market Prices Of Similar Liabilities [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  |  | 74.00%
Variable Interest Entity Primary Beneficiary [Member] | Maximum [Member] | Loans Receivable and Other Instruments at Fair Value [Member] | Impact Of Financial Guarantee [Member] | Market Prices of Similar Liabilities Adjusted for Financial Guarantees Provided to VIE Obligations [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  | 27.00% | 27.00%
Variable Interest Entity Primary Beneficiary [Member] | Weighted Average [Member] | Variable Interest Entity Notes [Member] | Impact Of Financial Guarantee [Member] | Market Prices Of VIE Assets Adjusted For Financial Guarantees Provided Or Market Prices Of Similar Liabilities [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage | [3] |  | 74.00%
Variable Interest Entity Primary Beneficiary [Member] | Weighted Average [Member] | Loans Receivable and Other Instruments at Fair Value [Member] | Impact Of Financial Guarantee [Member] | Market Prices of Similar Liabilities Adjusted for Financial Guarantees Provided to VIE Obligations [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage | [4] | 27.00% | 27.00%
[1] | Range for EBITDA multiples, discount rate, weightings, hard asset values and type certificate values are not meaningful.
[2] | Ranges for discount rate, EBITDA multiple and EBITDA royalty share are not meaningful.
[3] | Weighted average represents the total MBIA guarantees as a percentage of total instrument fair value.S
[4] | Weighted average represents the total MBIA guarantees as a percentage of total instrument fair value.

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