XML 82 R71.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Commitments and Contingencies (Narrative) (Detail) $ in Millions | Jun. 30, 2018 USD ($) Lawsuits
--- | ---
Commitments and Contingencies [Abstract] |
Other material lawsuits pending | Lawsuits | 0
Operating leases future minimum payments due | $ | $ 35
Pledged Sales Tax Base Amount [Member] |
Loss Contingencies [Line Items] |
COFINA and PR Commonwealth settlement percentage | 53.65%
Cash Held In Trust BONY Mellon [Member] |
Loss Contingencies [Line Items] |
COFINA and PR Commonwealth settlement percentage | 100.00%

X
- Definition Other material lawsuits pending + References No definition available. + Details
Name: | mbi_NumberOfOtherLawsuits
Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
Name: | mbi_SettlementPercentage
Namespace Prefix: | mbi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 3) -URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717 + Details
Name: | us-gaap_OperatingLeasesFutureMinimumPaymentsDue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_ConsolidatedEntitiesAxis=mbi_PledgedsalestaxbaseamountMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ConsolidatedEntitiesAxis=mbi_CashHeldInTrustBonyMellonMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |