Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Gross loss and loss expense reserves, beginning of period	$ 4,289	$ 4,179	$ 4,280	$ 4,137
Less reinsurance receivable	352	326	375	326
Net loss and loss expense reserves, beginning of period	3,937	3,853	3,905	3,811
Current accident year	725	853	1,380	1,442
Prior accident years	(85)	(96)	(201)	(155)
Total incurred	640	757	1,179	1,287
Current accident year	282	391	414	522
Prior accident years	290	248	665	608
Total paid	572	639	1,079	1,130
Net loss and loss expense reserves, end of period	4,005	3,971	4,005	3,971
Plus reinsurance receivable	332	508	332	508
Gross loss and loss expense reserves, end of period	$ 4,337	$ 4,479	$ 4,337	$ 4,479