Loss And Loss Adjustment Expense Reserves (Summary Of Credit Impairments Related To Derivatives) (Narrative) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014 securityloan	Mar. 31, 2013
Loss And Loss Adjustment Expense Reserves [Line Items]
Proprietary performance data on CRE loans, amount from 1992 to 2011	80,000
Additional estimated credit impairment on Cmbs derivatives	$ 20,000,000
Aggregate ITD credit impairment on Cmbs derivatives since 2010	4,200,000,000
Policyholder (Benefits) And Claims Incurred Net	$ 50,000,000	$ (194,000,000)
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%