Reinsurance - Earned Consolidated Property Casualty Insurance Premiums on Assumed and Ceded Business (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reinsurance Disclosures [Abstract]
Direct earned premiums	$ 1,002	$ 898	$ 2,895	$ 2,605
Assumed earned premiums	3	1	8	7
Ceded earned premiums	(51)	(48)	(150)	(137)
Net earned premiums	$ 954	$ 851	$ 2,753	$ 2,475