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	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Remedial Actions For Insured Obligations [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Loss adjustment expense incurred, gross	$ 18	$ 75