Loss And Loss Adjustment Expense Reserves (Summary Of Credit Impairments Related To Derivatives) (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014 securityloan	Jun. 30, 2013	Jun. 30, 2014 securityloan	Jun. 30, 2013
Loss And Loss Adjustment Expense Reserves [Line Items]
Proprietary performance data on CRE loans, amount from 1992 to 2011	80,000		80,000
Additional estimated credit impairment on Cmbs derivatives			$ 82
Policyholder (Benefits) And Claims Incurred Net	$ 12	$ 188	$ 62	$ (6)
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%