Identifiable Assets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 16,022	$ 15,635
Property, Liability and Casualty Insurance Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,277	2,272
Life Insurance Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	1,230	1,237
Investments Segment
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	12,223	11,883
Other
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 292	$ 243