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Loss and Loss Adjustment Expense Reserves (Schedule of Insurance Loss Recoverable) (Detail) - Insurance Loss Recoverable [Member] $ in Millions | 9 Months Ended
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Sep. 30, 2023 USD ($)
Roll forward of Insurance Loss Recoverable [Line Items] |
Gross Reserve beginning balance, Insurance loss recoverable | $ 137
Collections for Cases | (7)
Accretion of Recoveries | 3
Changes in Discount Rates | 1
Changes in Assumptions | 43
Gross Reserve ending balance, Insurance loss recoverable | $ 177

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- Definition Cash receipts related to recoveries of previously paid claims + References No definition available. + Details
Name: | mbi_CollectionsForCases
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Carrying amount as of the balance sheet date of paid insurance policy claims and LAE expense expected to be recovered. + References No definition available. + Details
Name: | mbi_InsuranceLossRecoverable
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Insurance Loss Recoverable And Changes In Recoveries Of Unpaid Losses Accretion Of Recoveries + References No definition available. + Details
Name: | mbi_InsuranceLossRecoverableAndChangesInRecoveriesOfUnpaidLossesAccretionOfRecoveries
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Insurance Loss Recoverable And Changes In Recoveries Of Unpaid Losses Change In Assumptions + References No definition available. + Details
Name: | mbi_InsuranceLossRecoverableAndChangesInRecoveriesOfUnpaidLossesChangeInAssumptions
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Insurance Loss Recoverable And Changes In Recoveries Of Unpaid Losses Change In Discount Rate + References No definition available. + Details
Name: | mbi_InsuranceLossRecoverableAndChangesInRecoveriesOfUnpaidLossesChangeInDiscountRate
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Roll forward of Insurance Loss Recoverable [Line Items] + References No definition available. + Details
Name: | mbi_RollForwardOfInsuranceLossRecoverableLineItems
Namespace Prefix: | mbi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | mbi_ClaimLiabilityAxis=mbi_InsuranceLossRecoverableMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |