This element represents the gross amount of claim payments during the period

No definition available.

Name:	mbi_ClaimPayments
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Outstanding insured bonds.

+ References

No definition available.

+ Details

Name:	mbi_OutstandingInsuredBonds
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479907/805-20-50-5

+ Details

Name:	us-gaap_BusinessAcquisitionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the provision for expected and allowed claims included in liabilities subject to compromise.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 852
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481404/852-10-50-2

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-18

+ Details

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=mbi_PuertoRicoElectricPowerAuthorityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=mbi_NationalPublicFinanceGuaranteeCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions		3 Months Ended
	Jan. 01, 2024 USD ($)	Mar. 31, 2024 USD ($) Segments	Jun. 26, 2023 USD ($)
Business Acquisition [Line Items]
Number of operating segments \| Segments		3
Puerto Rico Electric Power Authority [Member]
Business Acquisition [Line Items]
Outstanding insured bonds		$ 792
Maximum [Member]
Business Acquisition [Line Items]
Liabilities Subject to Compromise, Provision for Expected and Allowed Claims			$ 7,600
Minimum [Member]
Business Acquisition [Line Items]
Liabilities Subject to Compromise, Provision for Expected and Allowed Claims			$ 2,400
National Public Finance Guarantee Corporation [Member] \| Puerto Rico Electric Power Authority [Member]
Business Acquisition [Line Items]
Claims payments	$ 16