Incurred Consolidated Property Casualty Insurance Loss and Loss Expenses on Assumed and Ceded Business (Detail) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Net incurred loss and loss expenses	$ 656	$ 575	$ 2,032	$ 1,686
Property, Liability and Casualty Insurance Segment
Direct incurred loss and loss expenses	649	549	2,157	1,526
Assumed incurred loss and loss expenses	8	3	28	8
Ceded incurred loss and loss expenses	(50)	(21)	(291)	23
Net incurred loss and loss expenses	$ 607	$ 531	$ 1,894	$ 1,557