Identifiable Assets (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 16,479	$ 15,635
Property, Liability and Casualty Insurance Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,294	2,272
Life Insurance Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,200	1,237
Investments Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	12,582	11,883
Other Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 403	$ 243