Acceleration and commutation payment.

No definition available.

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

- Definition

Bonds issued.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Conditional value instrument additional recoveries from the percentage of sales and usage tax receipts.

+ References

No definition available.

+ Details

Name:	mbi_ConditionalValueInstrumentAdditionalRecoveriesFromThePercentageOfSalesAndUsageTaxReceipts
Namespace Prefix:	mbi_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Disposal group discontinued operation loss gain.

+ References

No definition available.

+ Details

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

- Definition

Gain loss on assets and liabilities reclassified as held for sale.

+ References

No definition available.

+ Details

Name:	mbi_GainLossOnAssetsAndLiabilitiesReclassifiedAsHeldForSale
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Gross par outstanding.

+ References

No definition available.

+ Details

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

- Definition

Amount of outstanding bonds for a specific issuer

+ References

No definition available.

+ Details

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

- Definition

Proceeds from GO PSA.

+ References

No definition available.

+ Details

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

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

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 45
-Paragraph 20
-URI https://asc.fasb.org/extlink&oid=118262064&loc=SL116631418-115840

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 10
-URI https://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 45
-Paragraph 21
-URI https://asc.fasb.org/extlink&oid=118262064&loc=SL116631419-115840

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(1))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_Cash
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI https://asc.fasb.org/extlink&oid=126901519&loc=d3e8672-108599

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=mbi_GOPSAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=mbi_PuertoRicoHighwayAndTransportationAuthorityMember
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:	us-gaap_FinancialInstrumentAxis=mbi_GOAndPBAMember
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_ConsolidatedEntitiesAxis=mbi_NationalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_PR
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions			3 Months Ended	12 Months Ended
	Jan. 01, 2023 USD ($)	Mar. 15, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2022 USD ($) segments	Dec. 06, 2022 USD ($)	Jul. 08, 2022 USD ($)
Business Acquisition [Line Items]
Number of operating segments \| segments				3
Gain loss on assets and liabilities reclassified as held for sale				$ 0
Disposal Group Discontinued Operation Loss Gain			$ 54
GO PSA [Member]
Business Acquisition [Line Items]
Proceeds from GO PSA		$ 1,000
Puerto Rico Electric Power Authority [Member]
Business Acquisition [Line Items]
Outstanding bonds			$ 945	$ 945
National Public Finance Guarantee Corporation [Member] \| GO PSA [Member]
Business Acquisition [Line Items]
Conditional value instrument additional recoveries from the percentage of sales and usage tax receipts			5.50%	5.50%
Acceleration and commutation payment				$ 277
National Public Finance Guarantee Corporation [Member] \| Puerto Rico Highway and Transportation Authority [Member]
Business Acquisition [Line Items]
Acceleration and commutation payment				556
Cash					$ 46	$ 33
Expected bonds issued					$ 177	$ 358
Maximum [Member] \| National Public Finance Guarantee Corporation [Member] \| GO and PBA [Member]
Business Acquisition [Line Items]
Outstanding bonds			$ 0	0
Minimum [Member] \| National Public Finance Guarantee Corporation [Member] \| GO and PBA [Member]
Business Acquisition [Line Items]
Outstanding bonds			495	495
Gross par outstanding			380	380
National [Member] \| Maximum [Member] \| Puerto Rico Highway and Transportation Authority [Member]
Business Acquisition [Line Items]
Outstanding bonds			0	0
National [Member] \| Minimum [Member] \| Puerto Rico Highway and Transportation Authority [Member]
Business Acquisition [Line Items]
Outstanding bonds			910	910
Gross par outstanding			581	581
Puerto Rico [Member]
Business Acquisition [Line Items]
Claims payments				189
Outstanding bonds			$ 1,000	$ 1,000
Puerto Rico [Member] \| Subsequent Event [Member] \| National Public Finance Guarantee Corporation [Member]
Business Acquisition [Line Items]
Claims payments	$ 18