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Insurance Premiums (Narrative) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2024	Dec. 31, 2023
Insurance Premiums [Line Items]
Weighted average risk-free rate		3.00%	3.00%
Weighted average expected collection term of the premiums receivable, years		8 years 6 months 25 days	8 years 9 months
Reinsurance premiums payable	[1]	$ 14
Premiums [Member]
Insurance Premiums [Line Items]
Reinsurance premiums payable		$ 3	$ 4
[1] Represents a withdrawal of ratings.

X

- Definition

Insurance Premiums Line Items

+ References

No definition available.

+ Details

Name:	mbi_InsurancePremiumsLineItems
Namespace Prefix:	mbi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Weighted average period over which premium receivable for financial guarantee insurance contracts is collected where premium is received over the contract period, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 310
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(5)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477363/944-310-50-3

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodPremiumReceivableWeightedAverageCollectionPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Weighted-average risk-free rate used to discount amount of premium expected to be collected for financial guarantee insurance contract where premium is to be received over contract period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 310
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(4)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477363/944-310-50-3

+ Details

Name:	us-gaap_FinancialGuaranteeInsuranceContractsPremiumReceivedOverContractPeriodPremiumReceivableWeightedAverageRiskFreeDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The carrying amount as of the balance sheet date of the known and estimated amounts owed to insurers under reinsurance treaties or other arrangements.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_LongLivedAssetsHeldForSaleByAssetTypeAxis=mbi_PremiumsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: