Reinsurance - Earned Consolidated Property Casualty Insurance Premiums on Assumed and Ceded Business (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reinsurance Disclosures [Abstract]
Direct earned premiums	$ 958	$ 868	$ 1,893	$ 1,707
Assumed earned premiums	3	3	5	6
Ceded earned premiums	(51)	(45)	(99)	(89)
Net earned premiums	$ 910	$ 826	$ 1,799	$ 1,624