XML 62 R52.htm IDEA: XBRL DOCUMENT
v3.23.1

Investments (Narrative) (Detail) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2023 USD ($) security | Dec. 31, 2022 USD ($) security
Schedule Of Investments [Line Items] |  |
Fair value of securities on deposit with various regulatory authorities | $ | $ 10 | $ 10
Number of securities in unrealized loss position for a continuous 12 month period | security | 495 | 210
Rate that a security's fair value is below book value | 5.00% | 5.00%
Asset Pledged as Collateral [Member] |  |
Schedule Of Investments [Line Items] |  |
Fair value of securities pledged as collateral | $ | $ 228 | $ 251
Securities In Unrealized Loss Position [Member] |  |
Schedule Of Investments [Line Items] |  |
Weighted average contractual maturity period in years for securities in an unrealized loss position | 14 years | 14 years
Fair Value Below Book Value Greater Than Five Percent [Member] |  |
Schedule Of Investments [Line Items] |  |
Number of securities in unrealized loss position for a continuous 12 month period | security | 444 | 190

X
- Definition Fair Value Of Securities On Deposit With Various Regulatory Authorities + References No definition available. + Details
Name: | mbi_FairValueOfSecuritiesOnDepositWithVariousRegulatoryAuthorities
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Disclosure regarding factors used to determine that the impairment of securities not categorized as trading securities (hence equal to available for sale and held to maturity securities) where cost exceeds fair value. This item contains disclosure of the number of investment positions in the investments determined to be temporarily impaired. + References No definition available. + Details
Name: | mbi_InvestmentSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsForContinuousTwelveMonthPeriod
Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage that a security's fair value is below its book value on available-for-sale and held-to-maturity securities. This percentage is used as a severity threshold for disclosing information about securities in an unrealized loss position for a continuous 12 month period or longer. + References No definition available. + Details
Name: | mbi_PercentageOfSecuritiesBookValueExceededMarketValue
Namespace Prefix: | mbi_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition This element represents the weighted average contractual maturity period in years for securities in an unrealized loss position. + References No definition available. + Details
Name: | mbi_WeightedAverageContractualMaturityPeriodOfSecuritiesUnrealizedLossPosition
Namespace Prefix: | mbi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969 + Details
Name: | us-gaap_FinancialInstrumentsOwnedAtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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_ScheduleOfInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_PledgedStatusAxis=us-gaap_AssetPledgedAsCollateralMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | mbi_InvestmentNotesAxis=mbi_SecuritiesInUnrealizedLossPositionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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