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Loss And Loss Adjustment Expense Reserves (Summary Of Credit Impairments Related To Derivatives) (Narrative) (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Loss And Loss Adjustment Expense Reserves [Line Items]      
Additional estimated credit impairment on Cmbs derivatives $ 91mbi_AdditionalEstimatedCreditImpairmentOnCmbsDerivatives    
Policyholder (Benefits) And Claims Incurred Net $ 133us-gaap_PolicyholderBenefitsAndClaimsIncurredNet $ 117us-gaap_PolicyholderBenefitsAndClaimsIncurredNet $ 50us-gaap_PolicyholderBenefitsAndClaimsIncurredNet
Mbia Corp [Member]      
Loss And Loss Adjustment Expense Reserves [Line Items]      
Discount rate of credit impairments 5.17%mbi_DiscountRateOfCreditImpairments
/ dei_LegalEntityAxis
= mbi_MbiaCorpMember		    
MBIA UK [Member]      
Loss And Loss Adjustment Expense Reserves [Line Items]      
Discount rate of credit impairments 2.20%mbi_DiscountRateOfCreditImpairments
/ dei_LegalEntityAxis
= mbi_MbiaUkMember