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, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 4,219	$ 4,337	$ 4,169	$ 4,280
Less reinsurance receivable	333	332	356	375
Net loss and loss expense reserves, beginning of period	3,886	4,005	3,813	3,905
Current accident year	631	611	1,840	1,991
Prior accident years	(38)	(86)	(140)	(287)
Total incurred	593	525	1,700	1,704
Current accident year	329	364	699	778
Prior accident years	233	229	897	894
Total paid	562	593	1,596	1,672
Net loss and loss expense reserves, end of period	3,917	3,937	3,917	3,937
Plus reinsurance receivable	321	343	321	343
Gross loss and loss expense reserves, end of period	$ 4,238	$ 4,280	$ 4,238	$ 4,280