Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Gross loss and loss expense reserves, beginning of period	$ 4,479	$ 4,131	$ 4,137	$ 4,096
Less reinsurance receivable	508	311	326	435
Net loss and loss expense reserves, beginning of period	3,971	3,820	3,811	3,661
Current accident year	675	592	2,115	1,731
Prior accident years	(68)	(61)	(221)	(174)
Total incurred	607	531	1,894	1,557
Current accident year	360	308	878	641
Prior accident years	205	196	814	730
Total paid	565	504	1,692	1,371
Net loss and loss expense reserves, end of period	4,013	3,847	4,013	3,847
Plus reinsurance receivable	450	319	450	319
Gross loss and loss expense reserves, end of period	$ 4,463	$ 4,166	$ 4,463	$ 4,166