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Loss And Loss Adjustment Expense Reserves (RMBS Reserves) (Narrative) (Detail) (USD $) In Millions, unless otherwise specified | 1 Months Ended | 6 Months Ended
--- | --- | ---
May 31, 2013 | Jun. 30, 2013
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Charged-off loans recovery values |  | $ 0
Percentage of Current Roll to Loss for the transaction |  | 3.00%
June Two Thousand Thirteen To November Two Thousand Thirteen [Member] | Scenario Forecast [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Decrease in percentage of Current Roll to Loss for transaction |  | 25.00%
June Two Thousand Thirteen To November Two Thousand Thirteen [Member] | Scenario Forecast [Member] | Rate Reduction [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Decrease in percentage of Current Roll to Loss for transaction |  | 0.75%
December Thirty One Two Thousand Thirteen To June Thirty Two Thousand Fourteen [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Current Roll to Loss |  | 0.00%
First Lien R M B S Reserves [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Delinquency period charged off on transaction specific basis, days |  | 90
90+ day roll rate to loss set |  | 90.00%
First Lien R M B S Reserves [Member] | ALT-A [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Percentage of loss after declining over a 24-month period |  | 25.00%
First Lien R M B S Reserves [Member] | Foreclosure [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Assumed roll rate for loans |  | 90.00%
First Lien R M B S Reserves [Member] | Real Estate Owned [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Assumed roll rate for loans |  | 90.00%
First Lien R M B S Reserves [Member] | Bankruptcy [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Assumed roll rate for loans |  | 75.00%
Rmbs And Heloc And Ces [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Assumed roll rate for ninety plus day delinquent loans excluding foreclosure and real estate owned |  | 95.00%
Percentage of loans in 30-59 days delinquent bucket | 10.00% |
Percentage of loans charged-off | 30.00% |
Percentage of Current Roll to Loss for the transaction | 3.00% |
Addition to case basis reserves before considering potential recoveries for elevated delinquency and loss for stress case |  | 90
Change in recoveries of actual and expected payments related to ineligible mortgages |  | $ 308
Rmbs And Heloc And Ces [Member] | Scenario Forecast [Member] | Minimum [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Period of elevated delinquency and loss for stress case, additional months |  | 6
Rmbs And Heloc And Ces [Member] | Scenario Forecast [Member] | Maximum [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Period of elevated delinquency and loss for stress case, additional months |  | 24
Rmbs And Heloc And Ces [Member] | June Two Thousand Thirteen To November Two Thousand Thirteen [Member] |  |
Loss And Loss Adjustment Expense Reserves [Line Items] |  |
Period of elevated delinquency and loss for base case, beginning, months |  | 6

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- Definition Assumed Roll Rate For Loans + References No definition available. + Details
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Namespace Prefix: | mbi_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Assumed roll rate for ninety plus day delinquent loans exluding foreclosure and real estate owned + References No definition available. + Details
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Namespace Prefix: | mbi_
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- Definition Change In Recoveries Of Actual And Expected Payments Related To Ineligible Mortgages + References No definition available. + Details
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- Definition Charged Off Loan Recovery Value + References No definition available. + Details
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- Definition Delinquency Period Charged Off On A Transaction Specific Basis Days + References No definition available. + Details
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- Details
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- Definition Percentage Of Current Roll To Loss For Transaction + References No definition available. + Details
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- Definition Percentage Of Further Reduction Of Current Roll To Loss For Transaction + References No definition available. + Details
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- Definition Percentage Of Loans Charged Off + References No definition available. + Details
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- Definition Percentage Of Loans In 30-59 Day Delinquent Bucket + References No definition available. + Details
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Data Type: | num:percentItemType
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- Definition Percentage Of Roll Rate To Loss Set + References No definition available. + Details
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- Definition Period Of Elevated Delinquency And Loss For Stress Case, Additional Months + References No definition available. + Details
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