Unpaid Losses and Loss Expenses - Reconciliation of Beginning and Ending Liability for Unpaid Losses and Loss Expenses (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Insurance [Abstract]
Gross liability, beginning of year	$ 23,963	$ 23,068	$ 22,718
Reinsurance recoverable, beginning of year	1,941	1,739	1,817
Net liability, beginning of year	22,022	21,329	20,901
Net incurred losses and loss expenses related to [Abstract]
Current year	7,232	8,121	8,174
Prior years	(712)	(614)	(767)
Net incurred losses and loss expenses, total	6,520	7,507	7,407
Net payments for losses and loss expenses related to [Abstract]
Current year	2,150	2,323	2,746
Prior years	4,952	4,493	4,300
Net payments for losses and loss expenses, total	7,102	6,816	7,046
Foreign currency translation effect	(96)	2	67
Net liability, end of year	21,344	22,022	21,329
Reinsurance recoverable, end of year	1,802	1,941	1,739
Gross liability, end of year	$ 23,146	$ 23,963	$ 23,068