Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Gross loss and loss expense reserves, beginning of period	$ 4,179	$ 4,065	$ 4,137	$ 4,096
Less reinsurance receivable	326	343	326	435
Net loss and loss expense reserves, beginning of period	3,853	3,722	3,811	3,661
Current accident year	853	625	1,442	1,139
Prior accident years	(96)	(73)	(155)	(113)
Total incurred	757	552	1,287	1,026
Current accident year	391	221	522	333
Prior accident years	248	233	608	534
Total paid	639	454	1,130	867
Net loss and loss expense reserves, end of period	3,971	3,820	3,971	3,820
Plus reinsurance receivable	508	311	508	311
Gross loss and loss expense reserves, end of period	$ 4,479	$ 4,131	$ 4,479	$ 4,131