XML 46 R35.htm IDEA: XBRL DOCUMENT v3.8.0.1

Variable Interest Entities (Narrative) (Detail) $ in Billions	3 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Variable Interest Entity [Line Items]
Carrying amounts of assets	$ 3.2	$ 3.2
Carrying amounts of liabilities	$ 2.3	$ 2.3
Number of variable interest entities consolidated	0
Variable Interest Entity Primary Beneficiary [Member] | Zohar Funds Bankruptcy Cases Debtors [Member]
Variable Interest Entity [Line Items]
Number of VIEs	2

X

- Definition

Number of consolidated VIEs as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	mbi_NumberOfConsolidatedVariableInterestEntities
Namespace Prefix:	mbi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Represents the number of VIEs consolidated during the period.

+ References

No definition available.

+ Details

Name:	mbi_NumberOfVariableInterestEntitiesConsolidated
Namespace Prefix:	mbi_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5710-111685

+ Details

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

X

- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=77990344&loc=d3e5710-111685

+ Details

Name:	us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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

X

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_MajorCustomersAxis=mbi_ZoharFundsBankruptcyCasesDebtorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: