Loss And Loss Adjustment Expense Reserves (Schedule Of Total Estimated Recoveries From Ineligible Second-Lien Mortgage Loans) (Detail) (Ineligible Mortgage Loans [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Ineligible Mortgage Loans [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Total Estimated Recoveries from Ineligible Mortgage Loans, Beginning Balance	$ 3,119	$ 2,517
Accretion of Future Collections	36	65
Changes in Discount Rates	2	35
Recoveries (Collections)		(86)
Changes in Amount of Collections		29
Changes in Assumptions	426	559
Total Estimated Recoveries from Ineligible Mortgage Loans, Ending Balance	$ 3,583	$ 3,119