XML 35 R40.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Loss And Loss Adjustment Expense Reserves (Summary Of Credit Impairments Related To Derivatives) (Narrative) (Detail) (USD $) | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2013 securityloan | Sep. 30, 2012 | Sep. 30, 2013 securityloan | Sep. 30, 2012
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |
Discount rate of credit impairments |  |  | 5.72% |
Proprietary performance data on CRE loans, amount from 1992 to 2011 | 80,000 |  | 80,000 |
Additional estimated credit impairment on Cmbs derivatives |  |  | $ 487,000,000 |
Aggregate ITD credit impairment on Cmbs derivatives since 2010 |  |  | 4,100,000,000 |
Cmbs severities exceeded complete loss in certain instances |  |  | 100.00% |
Losses and loss adjustment | 98,000,000 | 171,000,000 | 92,000,000 | 330,000,000
Commercial Real Estate Collateralized Debt Obligations [Member] |  |  |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |
Losses and loss adjustment |  |  | $ 28,000,000 |
Minimum [Member] |  |  |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |
Percentage of loss on liquidation |  |  | 1.00% |
Maximum [Member] |  |  |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |  |  |
Percentage of loss on liquidation |  |  | 2.00% |

X
- Definition Additional Estimated Credit Impairment On Cmbs Derivatives + References No definition available. + Details
Name: | mbi_AdditionalEstimatedCreditImpairmentOnCmbsDerivatives
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Aggregate ITD Credit Impairment On Cmbs Derivatives + References No definition available. + Details
Name: | mbi_AggregateITDCreditImpairmentOnCmbsDerivatives
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This element represents Cmbs severities exceeded complete loss in certain instances. + References No definition available. + Details
Name: | mbi_CmbsSeveritiesExceededCompleteLossInCertainInstances
Namespace Prefix: | mbi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Discount Rate Of Credit Impairments + References No definition available. + Details
Name: | mbi_DiscountRateOfCreditImpairments
Namespace Prefix: | mbi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | mbi_LossAndLossAdjustmentExpenseReservesLineItems
Namespace Prefix: | mbi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage Of Loss On Liquidation + References No definition available. + Details
Name: | mbi_PercentageOfLossOnLiquidation
Namespace Prefix: | mbi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Proprietary Performance Data On CRE Loans Amount + References No definition available. + Details
Name: | mbi_ProprietaryPerformanceDataOnCreLoansAmount
Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.5) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 5 -Article 7 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6811-158387 + Details
Name: | us-gaap_PolicyholderBenefitsAndClaimsIncurredNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration