Property Casualty Loss And Loss Expenses (Consolidated Property Casualty Loss And Loss Expense Reserves) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property Casualty Loss And Loss Expenses [Abstract]
Gross loss and loss expense reserves, January 1	$ 4,280	$ 4,137	$ 4,096
Less reinsurance receivable	375	326	435
Net loss and loss expense reserves, January 1	3,905	3,811	3,661
Current accident year	2,533	2,620	2,319
Prior accident years	(396)	(285)	(304)
Total incurred	2,137	2,335	2,015
Current accident year	1,123	1,206	939
Prior accident years	1,106	1,035	926
Total paid	2,229	2,241	1,865
Net loss and loss expense reserves, December 31	3,813	3,905	3,811
Plus reinsurance receivable	356	375	326
Gross loss and loss expense reserves, December 31	$ 4,169	$ 4,280	$ 4,137