Reinsurance - Effect of Reinsurance on Premiums Written and Earned (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Insurance [Abstract]
Direct premiums written	$ 12,804	$ 12,647	$ 12,452
Assumed reinsurance	503	423	398
Ceded reinsurance	(1,083)	(1,200)	(1,092)
Net premiums written	12,224	11,870	11,758
Direct premiums earned	12,717	12,596	12,387
Assumed reinsurance	476	422	365
Ceded reinsurance	(1,127)	(1,180)	(1,108)
Net premiums earned	$ 12,066	$ 11,838	$ 11,644