Loss And Loss Adjustment Expense Reserves (Schedule Of Expenses Related To Remedial Actions For Insured Obligations) (Detail) (Remedial Actions For Insured Obligations [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Remedial Actions For Insured Obligations [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss adjustment expense incurred, gross	$ 137	$ 120	$ 91