XML 83 R67.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Investments (Narrative) (Detail) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 USD ($) security | Dec. 31, 2020 USD ($) security
Schedule Of Investments [Line Items] |  |
Fair value of securities on deposit with various regulatory authorities | $ | $ 11 | $ 11
Fair value of securities pledged as collateral | $ | $ 280 | $ 282
Number of securities in unrealized loss position for a continuous 12 month period | security | 36 | 42
Rate that a security's fair value is below book value | 5.00% | 5.00%
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 | 11 years | 9 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 | 7 | 9

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 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
- Definition Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 50 -Paragraph 1A -Subparagraph (b)(1)(i) -URI http://asc.fasb.org/extlink&oid=109249958&loc=SL6224234-111729 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728 + Details
Name: | us-gaap_SecurityOwnedAndPledgedAsCollateralFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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: |