Reinsurance (Incurred Consolidated Property Casualty Insurance Loss And Loss Expenses On Assumed And Ceded Business) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net incurred loss and loss expenses	$ 2,322	$ 2,524	$ 2,180
Property, Liability And Casualty Insurance Segment [Member]
Direct incurred loss and loss expenses	2,235	2,588	2,003
Assumed incurred loss and loss expenses	6	24	11
Ceded incurred loss and loss expenses	(104)	(277)	(4)
Net incurred loss and loss expenses	$ 2,137	$ 2,335	$ 2,010