XML 76 R83.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Investments (Distribution Of Securities By Percentage Of Fair Value Below Book Value By More Than 5%) (Detail) (USD $) In Millions, unless otherwise specified | Dec. 31, 2012 Security
--- | ---
>5% to 15% [Member] |
Schedule of Investments [Line Items] |
Number of Securities | 31
Book Value | $ 309
Fair Value | 278
Percentage Book Value Exceeded Market Value, Minimum | 5.00%
Percentage Book Value Exceeded Market Value, Maximum | 15.00%
>15% to 25% [Member] |
Schedule of Investments [Line Items] |
Number of Securities | 18
Book Value | 682
Fair Value | 549
Percentage Book Value Exceeded Market Value, Minimum | 15.00%
Percentage Book Value Exceeded Market Value, Maximum | 25.00%
>25% to 50% [Member] |
Schedule of Investments [Line Items] |
Number of Securities | 13
Book Value | 69
Fair Value | 45
Percentage Book Value Exceeded Market Value, Minimum | 25.00%
Percentage Book Value Exceeded Market Value, Maximum | 50.00%
> 50% [Member] |
Schedule of Investments [Line Items] |
Number of Securities | 27
Book Value | 87
Fair Value | 18
Percentage Book Value Exceeded Market Value, Minimum | 50.00%
Greater Than 5% [Member] |
Schedule of Investments [Line Items] |
Number of Securities | 89
Book Value | 1,147
Fair Value | $ 890

X
- Definition Disclosure regarding factors used to determine that the impairment of securities not categorized as trading securities (hence equal to available for sale and held to maturity securities) where cost exceeds fair value. This item contains disclosure of the number of investment positions in the investments determined to be temporarily impaired. + References No definition available. + Details
Name: | mbi_InvestmentSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions
Namespace Prefix: | mbi_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Investments Securities In Unrealized Loss Position For Continuous Twelve Month Period or Longer At Fair Value + References No definition available. + Details
Name: | mbi_InvestmentsSecuritiesInUnrealizedLossPositionForContinuousTwelveMonthPeriodOrLongerAtFairValue
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Investments Securities In Unrealized Loss Position For Continuous Twelve Month Period or Longer Book Value + References No definition available. + Details
Name: | mbi_InvestmentsSecuritiesInUnrealizedLossPositionForContinuousTwelveMonthPeriodOrLongerBookValue
Namespace Prefix: | mbi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Percentage Book Value Exceeded Market Value, Maximum + References No definition available. + Details
Name: | mbi_PercentageBookValueExceededMarketValueMaximum
Namespace Prefix: | mbi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage Book Value Exceeded Market Value, Minimum + References No definition available. + Details
Name: | mbi_PercentageBookValueExceededMarketValueMinimum
Namespace Prefix: | mbi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_ScheduleOfInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration