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Commitments and Contingencies (Narrative) (Detail) $ in Millions | Mar. 31, 2025 USD ($) LegalProceedings
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Commitments And Contingencies [Line Items] |
Other material legal proceedings pending | LegalProceedings | 0
MBIA Corp [Member] | Fully Drawn [Member] |
Commitments And Contingencies [Line Items] |
Other Commitment | $ | $ 15

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- Definition CommitmentsAndContingenciesDisclosureAbstract + References No definition available. + Details
Name: | mbi_CommitmentsAndContingenciesLineItems
Namespace Prefix: | mbi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Other material legal proceedings pending. + References No definition available. + Details
Name: | mbi_NumberOfOtherLegalProceedings
Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions. + References No definition available. + Details
Name: | us-gaap_OtherCommitment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | srt_ConsolidatedEntitiesAxis=mbi_MbiaCorpMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=mbi_FullyDrawnMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |