Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 4,408	$ 4,219	$ 4,241	$ 4,169
Less reinsurance receivable	282	333	299	356
Net loss and loss expense reserves, beginning of period	4,126	3,886	3,942	3,813
Current accident year	647	631	2,125	1,840
Prior accident years	(25)	(38)	(120)	(140)
Total incurred	622	593	2,005	1,700
Current accident year	353	329	859	699
Prior accident years	286	233	979	897
Total paid	639	562	1,838	1,596
Net loss and loss expense reserves, end of period	4,109	3,917	4,109	3,917
Plus reinsurance receivable	284	321	284	321
Gross loss and loss expense reserves, end of period	$ 4,393	$ 4,238	$ 4,393	$ 4,238