Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue	$ 392		$ 443
Changes in LAE reserves	169		(109)
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss andLAE reserve, beginning balance	853
Loss payments for cases with reserves	(293)
Accretion of claim liability discount	10
Changes in discount rates	(71)
Changes in assumptions	116
Changes in unearned premium revenue	2
Changes in LAE reserves	(10)
Other	81	[1]
Gross loss andLAE reserve, ending balance	$ 688

[1] Primarily changes in amount and timing of payments.