Earned Consolidated Property Casualty Insurance Premiums on Assumed and Ceded Business (Detail) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Direct earned premiums	$ 807	$ 769	$ 1,587	$ 1,513
Assumed earned premiums	2	2	7	5
Ceded earned premiums	(79)	(43)	(119)	(82)
Net earned premiums	$ 730	$ 728	$ 1,475	$ 1,436