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Fair Value Of Financial Instruments (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - Fair Value Inputs Level 3 [Member] - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2023 | Mar. 31, 2022
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | $ 216 | $ 104
Total gains/(losses) included in earnings, assets |  | 9 | 2
Unrealized gains/(losses) included in OCI, assets | [1] | 0 | 0
Purchases, assets |  | 0 | 38
Issuances, assets |  | 0 | 0
Settlements, assets |  | (2) | (6)
Sales, assets |  | (16) | 0
Transfers into level 3, assets |  | 1 | 0
Transfers out of level 3, assets |  | 0 | 0
Ending balance, fair value assets |  | 208 | 138
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 6 | 0
Change in unrealized gains/(losses) for the period included in OCI for Liabilities still held | [1] | 0 | 0
Beginning balance, fair value liabilities |  | 219 | 389
Total (gains)/losses included in earnings, liabilities |  | 23 | (4)
Unrealized (gains)/losses included in OCI, liabilities | [2] | (16) | 10
Purchases, liabilities |  | 0 | 0
Issuances, liabilities |  | 0 | 0
Settlements, liabilities |  | (1) | (11)
Sales, liabilities |  | (18) | 0
Transfers into Level 3, liabilities |  | 0 | 0
Transfers out of Level 3, liabilities |  | 0 | 0
Ending balance, fair value liabilities |  | 207 | 384
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 9 | (11)
Change in Unrealized Gains/ (Losses) for the Period Included in OCI for Liabilities still held | [2] | (2) | 13
Loans receivable - residential [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 78 | 77
Total gains/(losses) included in earnings, assets |  | 7 | 1
Unrealized gains/(losses) included in OCI, assets | [1] | 0 | 0
Purchases, assets |  | 0 | 0
Issuances, assets |  | 0 | 0
Settlements, assets |  | (2) | (2)
Sales, assets |  | 0 | 0
Transfers into level 3, assets |  | 0 | 0
Transfers out of level 3, assets |  | 0 | 0
Ending balance, fair value assets |  | 83 | 76
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 5 | (1)
Change in unrealized gains/(losses) for the period included in OCI for Liabilities still held | [1] | 0 | 0
Residential Mortgage-Backed Non-Agency [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  |  | 0
Total gains/(losses) included in earnings, assets |  |  | 0
Unrealized gains/(losses) included in OCI, assets | [1] |  | 0
Purchases, assets |  |  | 38
Issuances, assets |  |  | 0
Settlements, assets |  |  | 0
Sales, assets |  |  | 0
Transfers into level 3, assets |  |  | 0
Transfers out of level 3, assets |  |  | 0
Ending balance, fair value assets |  |  | 38
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  |  | 0
Change in unrealized gains/(losses) for the period included in OCI for Liabilities still held | [1] |  | 0
Corporate Obligations [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 0 |
Total gains/(losses) included in earnings, assets |  | 0 |
Unrealized gains/(losses) included in OCI, assets | [1] | 0 |
Purchases, assets |  | 0 |
Issuances, assets |  | 0 |
Settlements, assets |  | 0 |
Sales, assets |  | 0 |
Transfers into level 3, assets |  | 1 |
Transfers out of level 3, assets |  | 0 |
Ending balance, fair value assets |  | 1 |
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 0 |
Change in unrealized gains/(losses) for the period included in OCI for Liabilities still held | [1] | 0 |
Equity investments [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 115 |
Total gains/(losses) included in earnings, assets |  | 0 |
Unrealized gains/(losses) included in OCI, assets | [1] | 0 |
Purchases, assets |  | 0 |
Issuances, assets |  | 0 |
Settlements, assets |  | 0 |
Sales, assets |  | 0 |
Transfers into level 3, assets |  | 0 |
Transfers out of level 3, assets |  | 0 |
Ending balance, fair value assets |  | 115 |
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 0 |
Change in unrealized gains/(losses) for the period included in OCI for Liabilities still held | [1] | 0 |
Collateralized Debt Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  |  | 4
Total gains/(losses) included in earnings, assets |  |  | 0
Unrealized gains/(losses) included in OCI, assets | [1] |  | 0
Purchases, assets |  |  | 0
Issuances, assets |  |  | 0
Settlements, assets |  |  | (4)
Sales, assets |  |  | 0
Transfers into level 3, assets |  |  | 0
Transfers out of level 3, assets |  |  | 0
Ending balance, fair value assets |  |  | 0
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  |  | 0
Change in unrealized gains/(losses) for the period included in OCI for Liabilities still held | [1] |  | 0
Medium Term Notes [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value liabilities |  | 41 | 98
Total (gains)/losses included in earnings, liabilities |  | 3 | (8)
Unrealized (gains)/losses included in OCI, liabilities | [2] | (2) | 9
Purchases, liabilities |  | 0 | 0
Issuances, liabilities |  | 0 | 0
Settlements, liabilities |  | 0 | 0
Sales, liabilities |  | 0 | 0
Transfers into Level 3, liabilities |  | 0 | 0
Transfers out of Level 3, liabilities |  | 0 | 0
Ending balance, fair value liabilities |  | 42 | 99
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 3 | (8)
Change in Unrealized Gains/ (Losses) for the Period Included in OCI for Liabilities still held | [2] | (2) | 9
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value liabilities |  | 172 | 291
Total (gains)/losses included in earnings, liabilities |  | 15 | 4
Unrealized (gains)/losses included in OCI, liabilities | [2] | (14) | 1
Purchases, liabilities |  | 0 | 0
Issuances, liabilities |  | 0 | 0
Settlements, liabilities |  | (1) | (11)
Sales, liabilities |  | (18) | 0
Transfers into Level 3, liabilities |  | 0 | 0
Transfers out of Level 3, liabilities |  | 0 | 0
Ending balance, fair value liabilities |  | 154 | 285
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 1 | (3)
Change in Unrealized Gains/ (Losses) for the Period Included in OCI for Liabilities still held | [2] | 0 | 4
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  |  | 9
Total gains/(losses) included in earnings, assets |  |  | 0
Unrealized gains/(losses) included in OCI, assets | [1] |  | 0
Purchases, assets |  |  | 0
Issuances, assets |  |  | 0
Settlements, assets |  |  | 0
Sales, assets |  |  | 0
Transfers into level 3, assets |  |  | 0
Transfers out of level 3, assets |  |  | 0
Ending balance, fair value assets |  |  | 9
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  |  | 0
Change in unrealized gains/(losses) for the period included in OCI for Liabilities still held | [1] |  | 0
Beginning balance, fair value liabilities |  | 6 |
Total (gains)/losses included in earnings, liabilities |  | 5 |
Unrealized (gains)/losses included in OCI, liabilities | [2] | 0 |
Purchases, liabilities |  | 0 |
Issuances, liabilities |  | 0 |
Settlements, liabilities |  | 0 |
Sales, liabilities |  | 0 |
Transfers into Level 3, liabilities |  | 0 |
Transfers out of Level 3, liabilities |  | 0 |
Ending balance, fair value liabilities |  | 11 |
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 5 |
Change in Unrealized Gains/ (Losses) for the Period Included in OCI for Liabilities still held | [2] | 0 |
Other Assets [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Beginning balance, fair value assets |  | 23 | 14
Total gains/(losses) included in earnings, assets |  | 2 | 1
Unrealized gains/(losses) included in OCI, assets | [1] | 0 | 0
Purchases, assets |  | 0 | 0
Issuances, assets |  | 0 | 0
Settlements, assets |  | 0 | 0
Sales, assets |  | (16) | 0
Transfers into level 3, assets |  | 0 | 0
Transfers out of level 3, assets |  | 0 | 0
Ending balance, fair value assets |  | 9 | 15
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 1 | 1
Change in unrealized gains/(losses) for the period included in OCI for Liabilities still held | [1] | $ 0 | $ 0
[1] | Reported within the “Unrealized gains (losses) on available-for-sale securities” on MBIA’s Consolidated Statement of Comprehensive Income/Loss.
[2] | Reported within the “Instrument-specific credit risk of liabilities measured at fair value” on MBIA’s Consolidated Statement of Comprehensive Income/Loss.

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