XML 61 R50.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Fair Value Of Financial Instruments (Aggregate Fair Value And Remaining Contractual Principal Balance Outstanding On Fair Value Option) (Detail) - Variable Interest Entity [Member] - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items] |  |
Loans receivable, contractual outstanding principal | $ 2,270 | $ 2,296
Loans receivable, fair value | 1,662 | 1,679
Loans receivable, difference | 608 | 617
Residential Mortgage Loans [Member] |  |
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items] |  |
Loans receivable, contractual outstanding principal | 687 | 732
Loans receivable, 90 days or more past due, contractual outstanding principal | 189 | 170
Loans receivable, fair value | 686 | 727
Loans receivable, 90 days or more past due, fair value | 51 | 32
Loans receivable, difference | 1 | 5
Loans receivable, 90 days or more past due, difference | 138 | 138
Corporate Loans [Member] |  |
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items] |  |
Loans receivable, 90 days or more past due, contractual outstanding principal | 1,394 | 1,394
Loans receivable, 90 days or more past due, fair value | 925 | 920
Loans receivable, 90 days or more past due, difference | 469 | 474
Medium Term Notes [Member] |  |
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items] |  |
Long-term debt instruments, contractual outstanding principal | 184 | 180
Long-term debt instruments, fair value | 146 | 115
Long-term debt instruments, difference | 39 | 65
Variable Interest Entity Notes [Member] |  |
Schedule Of Fair Value Of Separate Accounts By Major Category Of Investment [Line Items] |  |
Long-term debt instruments, contractual outstanding principal | 1,848 | 1,882
Long-term debt instruments, fair value | 1,031 | 1,069
Long-term debt instruments, difference | $ 817 | $ 813

X
- Definition Fair Value Option Aggregate Fair Value Loans Receivable + References No definition available. + Details
Name: | mbi_FairValueOptionAggregateFairValueLoansReceivable
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair Value Option Aggregate Fair Value Long Term Debt Instruments + References No definition available. + Details
Name: | mbi_FairValueOptionAggregateFairValueLongTermDebtInstruments
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair Value Option Contractual Outstanding Principal Loans Receivable + References No definition available. + Details
Name: | mbi_FairValueOptionContractualOutstandingPrincipalLoansReceivable
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair Value Option Contractual Outstanding Principal Long-Term Debt Instruments + References No definition available. + Details
Name: | mbi_FairValueOptionContractualOutstandingPrincipalLongTermDebtInstruments
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair Value Option Contractual Outstanding Principal Loans Receivable 90 Days or More Past Due + References No definition available. + Details
Name: | mbi_Fairvalueoptioncontractualoutstandingprincipalloansreceivable90daysormorepastdue
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of loans and long-term receivables (other than securities categorized as trading, available-for-sale or held-to-maturity) that have contractual principal amounts and for which the fair value option has been elected. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612 + Details
Name: | us-gaap_FairValueOptionAggregateDifferencesLoansAndLongTermReceivables
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of long-term debt instruments that have contractual principal amounts and for which the fair value option has been elected. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612 + Details
Name: | us-gaap_FairValueOptionAggregateDifferencesLongTermDebtInstruments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612 + Details
Name: | us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are 90 days or more past due. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (e)(3) -URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612 + Details
Name: | us-gaap_FairValueOptionLoansHeldAsAssets90DaysOrMorePastDueAggregateDifference
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_ScheduleOfFairValueOfSeparateAccountsByMajorCategoryOfInvestmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=mbi_ResidentialMortgageLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=mbi_OtherLoansMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_MediumTermNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=mbi_VariableInterestEntityNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |