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Variable Interest Entities (Narrative) (Detail) - Variable Interest Entity Primary Beneficiary [Member] - Structured Finance and International Insurance [Member] $ in Millions | 3 Months Ended
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Mar. 31, 2023 USD ($) | Mar. 31, 2022
Variable Interest Entity [Line Items] |  |
Number of variable interest entities deconsolidated | 1 | 0
Recorded Due To Credit Losses in AOCI [Member] |  |
Variable Interest Entity [Line Items] |  |
Net realized gains (losses) related to deconsolidation | $ (15) |

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- Definition Represents the number of VIEs deconsolidated during the period. + References No definition available. + Details
Name: | mbi_NumberOfVariableInterestEntitiesDeconsolidated
Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition The gain (loss) recognized on initial consolidation of a variable interest entity (VIE) when the VIE is not a business (as defined). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -URI https://asc.fasb.org/extlink&oid=123419778&loc=d3e5710-111685 + Details
Name: | us-gaap_VariableInterestEntityInitialConsolidationGainOrLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_VariableInterestEntityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=mbi_StructuredFinanceAndInternationalInsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | mbi_EventAxis=mbi_RecordedDueToCreditLossesInAociMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |