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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
 3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Loss And Loss Adjustment Expense Reserves [Line Items]        
Additional estimated credit impairment on Cmbs derivatives     $ 97  
Policyholder (Benefits) And Claims Incurred Net $ 20 $ 98 $ 82 $ 92
Mbia Corp [Member]
        
Loss And Loss Adjustment Expense Reserves [Line Items]        
Discount rate of credit impairments     5.09%  
MBIA UK [Member]
        
Loss And Loss Adjustment Expense Reserves [Line Items]        
Discount rate of credit impairments     2.50%