Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Gross loss and loss expense reserves, beginning of period	$ 4,337	$ 4,479	$ 4,280	$ 4,137
Less reinsurance receivable	332	508	375	326
Net loss and loss expense reserves, beginning of period	4,005	3,971	3,905	3,811
Current accident year	611	675	1,991	2,115
Prior accident years	(86)	(68)	(287)	(221)
Total incurred	525	607	1,704	1,894
Current accident year	364	360	778	878
Prior accident years	229	205	894	814
Total paid	593	565	1,672	1,692
Net loss and loss expense reserves, end of period	3,937	4,013	3,937	4,013
Plus reinsurance receivable	343	450	343	450
Gross loss and loss expense reserves, end of period	$ 4,280	$ 4,463	$ 4,280	$ 4,463