Loss And Loss Adjustment Expense Reserves (Summary Of Credit Impairments Related To Derivatives) (Narrative) (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013 securityloan	Sep. 30, 2012	Sep. 30, 2013 securityloan	Sep. 30, 2012
Loss And Loss Adjustment Expense Reserves [Line Items]
Discount rate of credit impairments			5.72%
Proprietary performance data on CRE loans, amount from 1992 to 2011	80,000		80,000
Additional estimated credit impairment on Cmbs derivatives			$ 487,000,000
Aggregate ITD credit impairment on Cmbs derivatives since 2010			4,100,000,000
Cmbs severities exceeded complete loss in certain instances			100.00%
Losses and loss adjustment	98,000,000	171,000,000	92,000,000	330,000,000
Commercial Real Estate Collateralized Debt Obligations [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and loss adjustment			$ 28,000,000
Minimum [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Percentage of loss on liquidation			1.00%
Maximum [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Percentage of loss on liquidation			2.00%