XML 86 R73.htm IDEA: XBRL DOCUMENT
v3.22.4

Investments (Distribution Of Securities By Percentage Of Fair Value Below Book Value By More Than 5% For A Continuous Twelve Month Period Or Longer) (Detail) - Unrealized loss position > 12 months $ in Millions | Dec. 31, 2022 USD ($) security
--- | ---
> 5% To 15% [Member] |
Available For Sale Securities [Abstract] |
Number of securities | security | 72
Book Value | $ 129
Fair Value | $ 117
Held To Maturity Securities [Abstract] |
Percentage Of Fair Value Below Book Value Minimum | 5.00%
Percentage Of Fair Value Below Book Value Maximum | 15.00%
> 15% To 25% [Member] |
Available For Sale Securities [Abstract] |
Number of securities | security | 63
Book Value | $ 117
Fair Value | $ 93
Held To Maturity Securities [Abstract] |
Percentage Of Fair Value Below Book Value Minimum | 15.00%
Percentage Of Fair Value Below Book Value Maximum | 25.00%
> 25% To 50% [Member] |
Available For Sale Securities [Abstract] |
Number of securities | security | 53
Book Value | $ 84
Fair Value | $ 56
Held To Maturity Securities [Abstract] |
Percentage Of Fair Value Below Book Value Minimum | 25.00%
Percentage Of Fair Value Below Book Value Maximum | 50.00%
> 50% [Member] |
Available For Sale Securities [Abstract] |
Number of securities | security | 2
Book Value | $ 0
Fair Value | $ 0
Held To Maturity Securities [Abstract] |
Percentage Of Fair Value Below Book Value Minimum | 50.00%
Greater Than 5% [Member] |
Available For Sale Securities [Abstract] |
Number of securities | security | 190
Book Value | $ 330
Fair Value | $ 266

X
- Definition Percentage Of Fair Value Below Book Value Maximum + References No definition available. + Details
Name: | mbi_PercentageOfFairValueBelowBookValueMaximum
Namespace Prefix: | mbi_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage Of Fair Value Below Book Value Minimum + References No definition available. + Details
Name: | mbi_PercentageOfFairValueBelowBookValueMinimum
Namespace Prefix: | mbi_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_AvailableForSaleSecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amortized cost, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostAfterAllowanceForCreditLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of investments in debt securities measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (b)(3) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (b)(3) -URI https://asc.fasb.org/extlink&oid=124269663&loc=SL82922888-210455 + Details
Name: | us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_HeldToMaturitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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

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

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

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=mbi_GreaterThanFiftyPercentMember
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: |