Incurred Consolidated Property Casualty Insurance Loss and Loss Expenses on Assumed and Ceded Business (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Reinsurance [Line Items]
Net incurred loss and loss expenses	$ 687	$ 801	$ 1,269	$ 1,376
Property, Liability and Casualty Insurance Segment
Reinsurance [Line Items]
Direct incurred loss and loss expenses	647	981	1,183	1,508
Assumed incurred loss and loss expenses	1	5	6	20
Ceded incurred loss and loss expenses	(8)	(229)	(10)	(241)
Net incurred loss and loss expenses	$ 640	$ 757	$ 1,179	$ 1,287