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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 | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value assets |  | $ 188 | $ 148 | $ 216 | $ 104
Total gains/(losses) included in earnings, assets |  | (7) | 4 | (7) | 1
Unrealized gains/(losses) included in OCI, assets | [1] | 0 | (2) | 0 | (6)
Purchases, assets |  | 0 | 102 | 0 | 161
Issuances, assets |  | 0 | 0 | 0 | 0
Settlements, assets |  | (2) | (2) | (7) | (10)
Sales, assets |  | (29) | (17) | (53) | (17)
Transfers into level 3, assets |  | 0 | 0 | 1 | 0
Transfers out of level 3, assets |  | 0 | 0 | 0 | 0
Ending balance, fair value assets |  | 150 | 233 | 150 | 233
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | (8) | 2 | (4) | (5)
Change in unrealized gains/(losses) for the period included in OCI for Assets still held, assets | [1] | 0 | (3) | 0 | 0
Beginning balance, fair value liabilities |  | 233 | 259 | 219 | 389
Total (gains)/losses included in earnings, liabilities |  | 11 | 30 | 51 | (16)
Unrealized (gains)/losses included in OCI, liabilities | [2] | (12) | (21) | (41) | 11
Purchases, liabilities |  | 0 | 0 | 0 | 0
Issuances, liabilities |  | 0 | 0 | 62 | 0
Settlements, liabilities |  | (21) | (52) | (45) | (168)
Sales, liabilities |  | (85) | 0 | (120) | 0
Transfers into Level 3, liabilities |  | 0 | 0 | 0 | 0
Transfers out of Level 3, liabilities |  | 0 | 0 | 0 | 0
Ending balance, fair value liabilities |  | 126 | 216 | 126 | 216
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | (2) | (5) | 6 | (32)
Change in Unrealized Gains/ (Losses) for the Period Included in OCI for Liabilities still held | [2] | 2 | 5 | (1) | 22
Loans receivable - residential [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value assets |  | 70 | 68 | 78 | 77
Total gains/(losses) included in earnings, assets |  | (7) | 13 | (10) | 8
Unrealized gains/(losses) included in OCI, assets | [1] | 0 | 0 | 0 | 0
Purchases, assets |  | 0 | 0 | 0 | 0
Issuances, assets |  | 0 | 0 | 0 | 0
Settlements, assets |  | (2) | (2) | (7) | (6)
Sales, assets |  | (29) | 0 | (29) | 0
Transfers into level 3, assets |  | 0 | 0 | 0 | 0
Transfers out of level 3, assets |  | 0 | 0 | 0 | 0
Ending balance, fair value assets |  | 32 | 79 | 32 | 79
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | (8) | 11 | (3) | 2
Change in unrealized gains/(losses) for the period included in OCI for Assets still held, assets | [1] | 0 | 0 | 0 | 0
Residential Mortgage-Backed Non Agency [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value assets |  |  | 55 |  | 0
Total gains/(losses) included in earnings, assets |  |  | 0 |  | 0
Unrealized gains/(losses) included in OCI, assets | [1] |  | (2) |  | (6)
Purchases, assets |  |  | 1 |  | 60
Issuances, assets |  |  | 0 |  | 0
Settlements, assets |  |  | 0 |  | 0
Sales, assets |  |  | (17) |  | (17)
Transfers into level 3, assets |  |  | 0 |  | 0
Transfers out of level 3, assets |  |  | 0 |  | 0
Ending balance, fair value assets |  |  | 37 |  | 37
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  |  | 0 |  | 0
Change in unrealized gains/(losses) for the period included in OCI for Assets still held, assets | [1] |  | (3) |  | 0
Corporate Obligations [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value assets |  | 1 |  | 0 |
Total gains/(losses) included in earnings, assets |  | 0 |  | 0 |
Unrealized gains/(losses) included in OCI, assets | [1] | 0 |  | 0 |
Purchases, assets |  | 0 |  | 0 |
Issuances, assets |  | 0 |  | 0 |
Settlements, assets |  | 0 |  | 0 |
Sales, assets |  | 0 |  | 0 |
Transfers into level 3, assets |  | 0 |  | 1 |
Transfers out of level 3, assets |  | 0 |  | 0 |
Ending balance, fair value assets |  | 1 |  | 1 |
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 0 |  | 0 |
Change in unrealized gains/(losses) for the period included in OCI for Assets still held, assets | [1] | 0 |  | 0 |
Equity investments [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value assets |  | 115 | 0 | 115 | 0
Total gains/(losses) included in earnings, assets |  | 0 | 0 | 0 | 0
Unrealized gains/(losses) included in OCI, assets | [1] | 0 | 0 | 0 | 0
Purchases, assets |  | 0 | 101 | 0 | 101
Issuances, assets |  | 0 | 0 | 0 | 0
Settlements, assets |  | 0 | 0 | 0 | 0
Sales, assets |  | 0 | 0 | 0 | 0
Transfers into level 3, assets |  | 0 | 0 | 0 | 0
Transfers out of level 3, assets |  | 0 | 0 | 0 | 0
Ending balance, fair value assets |  | 115 | 101 | 115 | 101
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 0 | 0 | 0 | 0
Change in unrealized gains/(losses) for the period included in OCI for Assets still held, assets | [1] | 0 | 0 | 0 | 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 |  | 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 Assets still held, assets | [1] |  |  |  | 0
Medium Term Notes [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value liabilities |  | 38 | 42 | 41 | 98
Total (gains)/losses included in earnings, liabilities |  | (3) | (8) | (2) | (29)
Unrealized (gains)/losses included in OCI, liabilities | [2] | 2 | 4 | (2) | 17
Purchases, liabilities |  | 0 | 0 | 0 | 0
Issuances, liabilities |  | 0 | 0 | 0 | 0
Settlements, liabilities |  | 0 |  | 0 | (48)
Sales, liabilities |  | 0 | 0 | 0 | 0
Transfers into Level 3, liabilities |  | 0 | 0 | 0 | 0
Transfers out of Level 3, liabilities |  | 0 | 0 | 0 | 0
Ending balance, fair value liabilities |  | 37 | 38 | 37 | 38
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | (3) | (8) | (2) | (28)
Change in Unrealized Gains/ (Losses) for the Period Included in OCI for Liabilities still held | [2] | 2 | 4 | (2) | 18
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value liabilities |  | 183 | 217 | 172 | 291
Total (gains)/losses included in earnings, liabilities |  | 15 | 33 | 48 | 8
Unrealized (gains)/losses included in OCI, liabilities | [2] | (14) | (25) | (39) | (6)
Purchases, liabilities |  | 0 | 0 | 0 | 0
Issuances, liabilities |  | 0 | 0 | 62 | 0
Settlements, liabilities |  | (21) | (52) | (45) | (120)
Sales, liabilities |  | (85) | 0 | (120) | 0
Transfers into Level 3, liabilities |  | 0 | 0 | 0 | 0
Transfers out of Level 3, liabilities |  | 0 | 0 | 0 | 0
Ending balance, fair value liabilities |  | 78 | 173 | 78 | 173
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | 2 | (2) | 3 | (9)
Change in Unrealized Gains/ (Losses) for the Period Included in OCI for Liabilities still held | [2] | 0 | 1 | 1 | 4
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value assets |  |  | 9 |  | 9
Total gains/(losses) included in earnings, assets |  |  | (9) |  | (9)
Unrealized gains/(losses) included in OCI, assets | [1] |  | 0 |  | 0
Purchases, assets |  |  | 0 |  | 0
Issuances, assets |  |  | 0 |  | 0
Settlements, assets |  |  | 0 |  | 0
Sales, assets |  |  | 0 |  | 0
Transfers into level 3, assets |  |  | 0 |  | 0
Transfers out of level 3, assets |  |  | 0 |  | 0
Ending balance, fair value assets |  |  | 0 |  | 0
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  |  | (9) |  | (9)
Change in unrealized gains/(losses) for the period included in OCI for Assets still held, assets | [1] |  | 0 |  | 0
Beginning balance, fair value liabilities |  | 12 | 0 | 6 | 0
Total (gains)/losses included in earnings, liabilities |  | (1) | 5 | 5 | 5
Unrealized (gains)/losses included in OCI, liabilities | [2] | 0 | 0 | 0 | 0
Purchases, liabilities |  | 0 | 0 | 0 | 0
Issuances, liabilities |  | 0 | 0 | 0 | 0
Settlements, liabilities |  | 0 | 0 | 0 | 0
Sales, liabilities |  | 0 | 0 | 0 | 0
Transfers into Level 3, liabilities |  | 0 | 0 | 0 | 0
Transfers out of Level 3, liabilities |  | 0 | 0 | 0 | 0
Ending balance, fair value liabilities |  | 11 | 5 | 11 | 5
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities |  | (1) | 5 | 5 | 5
Change in Unrealized Gains/ (Losses) for the Period Included in OCI for Liabilities still held | [2] | 0 | 0 | 0 | 0
Other Assets [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |  |
Beginning balance, fair value assets |  | 2 | 16 | 23 | 14
Total gains/(losses) included in earnings, assets |  | 0 | 0 | 3 | 2
Unrealized gains/(losses) included in OCI, assets | [1] | 0 | 0 | 0 | 0
Purchases, assets |  | 0 | 0 | 0 | 0
Issuances, assets |  | 0 | 0 | 0 | 0
Settlements, assets |  | 0 | 0 | 0 | 0
Sales, assets |  | 0 | 0 | (24) | 0
Transfers into level 3, assets |  | 0 | 0 | 0 | 0
Transfers out of level 3, assets |  | 0 | 0 | 0 | 0
Ending balance, fair value assets |  | 2 | 16 | 2 | 16
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets |  | 0 | 0 | 1 | 2
Change in unrealized gains/(losses) for the period included in OCI for Assets still held, assets | [1] | $ 0 | $ 0 | $ 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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- Definition Amount of unrealized gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3) and still held. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482106/820-10-50-2 + Details
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