Claim And Claim Adjustment Expense Reserves (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Claim And Claim Adjustment Expense Reserves [Line Items]
Catastrophe losses, net of reinsurance	$ 68	$ 100	$ 96	$ 155