Fair Value Of Financial Instruments (Narrative) (Detail) (USD $)	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of insured credit derivatives, value under Direct Price Model and Dual-Default Model	2.00%
Percentage of sector-specific transactions valued using BET model	8.00%
Percentage of transactions valued using corporate spreads used	48.00%
Percentage of transactions valued using spread benchmarked from most relevant spread source	44.00%
Percentage of transactions valued using WARF-sourced and/or ratings sourced credit spreads	78.00%
Net insured derivative liability	$ 1,200,000,000	$ 2,900,000,000
Impact of including the nonperformance risk in valuation of pre-tax net insured derivative liability	394,000,000	4,400,000,000
Percentage of level 3 assets at fair value in total assets measured at fair value value	22.00%	29.00%
Percentage of level 3 liabilities at fair value in total liabilities measured at fair value	61.00%	73.00%
Transfers into Level 3	403,000,000	293,000,000
Transfers out of Level 3	198,000,000	157,000,000
Transfers into Level 2	198,000,000	157,000,000
Transfers out of Level 2	403,000,000	293,000,000
Transfers into or out of Level 1	$ 0	$ 0
B E T Valuation Model [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Percentage of insured credit derivatives, fair value using the BET model	98.00%

Approximate percentage of level 3 assets at fair value in total assets measured at fair value.

No definition available.

Name:	mbi_ApproximatePercentageOfLevel3AssetsAtFairValueInTotalAssetsMeasuredAtFairValue
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Approximate percentage of level 3 liabilities at fair value in total liabilities measured at fair value.

+ References

No definition available.

+ Details

Name:	mbi_ApproximatePercentageOfLevel3LiabilitiesAtFairValueInTotalLiabilitiesMeasuredAtFairValue
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Impact Of Non Performance Risk On Insured Derivative Liability

+ References

No definition available.

+ Details

Name:	mbi_ImpactOfNonPerformanceRiskOnInsuredDerivativeLiability
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage Of Insured Credit Derivatives Value Under Bet Model

+ References

No definition available.

+ Details

Name:	mbi_PercentageOfInsuredCreditDerivativesValueUnderBetModel
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of insured credit derivatives value under direct price model and dual default model

+ References

No definition available.

+ Details

Name:	mbi_PercentageOfInsuredCreditDerivativesValueUnderDirectPriceModelAndDualDefaultModel
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage Of Sector Specific Transactions Valued Using BET Model

+ References

No definition available.

+ Details

Name:	mbi_PercentageOfSectorSpecificTransactionsValuedUsingBetModel
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage Of Transactions Valued Using Corporate Spread

+ References

No definition available.

+ Details

Name:	mbi_PercentageOfTransactionsValuedUsingCorporateSpread
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of Transactions Valued Using Spread Benchmark From Most Relevant Spread Source

+ References

No definition available.

+ Details

Name:	mbi_PercentageOfTransactionsValuedUsingSpreadBenchmarkFromMostRelevantSpreadSource
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of Transactions Valued Using Warf Sourced And Or Ratings Source Credit Spread

+ References

No definition available.

+ Details

Name:	mbi_PercentageOfTransactionsValuedUsingWarfSourcedAndOrRatingsSourceCreditSpread
Namespace Prefix:	mbi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Transfers of assets measured at fair value on a recurring basis into and out of level one during the period.

+ References

No definition available.

+ Details

Name:	mbi_TransfersIntoAndOutOfLevelOne
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Transfers of assets measured at fair value on a recurring basis into level three during the period.

+ References

No definition available.

+ Details

Name:	mbi_TransfersIntoLevelThree
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Transfers of assets measured at fair value on a recurring basis into level two during the period.

+ References

No definition available.

+ Details

Name:	mbi_TransfersIntoLevelTwo
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Transfers of assets measured at fair value on a recurring basis out of level three during the period.

+ References

No definition available.

+ Details

Name:	mbi_TransfersOutOfLevelThree
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Transfers of assets measured at fair value on a recurring basis out of level two during the period.

+ References

No definition available.

+ Details

Name:	mbi_TransfersOutOfLevelTwo
Namespace Prefix:	mbi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

+ Details

Name:	us-gaap_DerivativeAssetsLiabilitiesAtFairValueNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration