Identifiable Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 15,668	$ 15,095
Property, Liability and Casualty Insurance Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,298	2,008
Life Insurance Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,244	1,214
Investments Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	11,883	11,543
Other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 243	$ 330