Loss And Loss Adjustment Expense Reserves (Schedule Of Insurance Loss Recoverable And Changes In Recoveries On Unpaid Losses) (Detail) (Insurance Loss Recoverable And Changes In Recoveries On Unpaid Losses [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Insurance Loss Recoverable and Recoveries On Unpaid Losses [Line Items]
Collections for Cases with Recoveries	$ (13)	$ (101)
Accretion of Recoveries	39	73
Changes in Discount Rates	16	117
Changes in Timing of Collections
Changes in Amount of Collections	(145)	(227)
Changes in Assumptions	462	307
Changes in LAE Recoveries	13	12
Gross Reserve beginning balance, Total	3,608	3,427
Gross Reserve ending balance, Total	3,980	3,608
Insurance Loss Recoverable [Member]
Insurance Loss Recoverable and Recoveries On Unpaid Losses [Line Items]
Collections for Cases with Recoveries	(13)	(101)
Accretion of Recoveries	32	57
Changes in Discount Rates	4	49
Changes in Timing of Collections
Changes in Amount of Collections	(145)	(227)
Changes in Assumptions	700	723
Changes in LAE Recoveries	24	14
Gross Reserve beginning balance, Insurance loss recoverable	3,046	2,531
Gross Reserve ending balance, Insurance loss recoverable	3,648	3,046
Recoveries On Unpaid Losses [Member]
Insurance Loss Recoverable and Recoveries On Unpaid Losses [Line Items]
Collections for Cases with Recoveries
Accretion of Recoveries	7	16
Changes in Discount Rates	12	68
Changes in Timing of Collections
Changes in Amount of Collections
Changes in Assumptions	(238)	(416)
Changes in LAE Recoveries	(11)	(2)
Gross Reserve beginning balance, Recoveries on unpaid losses	562	896
Gross Reserve ending balance, Recoveries on unpaid losses	$ 332	$ 562