XML 30 R63.htm IDEA: XBRL DOCUMENT v3.20.1

Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (50)	$ (9)
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	(1)	14
Net gains (losses) on financial instruments at fair value and foreign exchange [Member | Interest Rate Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	(56)	(20)
Net gains (losses) on financial instruments at fair value and foreign exchange [Member | Currency Swaps Vie [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	10	(3)
Net gains (losses) on financial instruments at fair value and foreign exchange [Member | All Other [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (3)	$ 0

X

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959

+ Details

Name:	us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_IncomeStatementLocationAxis=mbi_UnrealizedGainsLossesOnInsuredDerivativesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CreditDefaultSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_IncomeStatementLocationAxis=mbi_ForeignExchangeAndOtherDerivativesFinancialInstrumentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=mbi_CurrencySwapsVieMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=mbi_AllOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: