Consolidated Supplementary Insurance Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs	$ 1,255	$ 1,206	$ 1,210
Unpaid Losses	23,146	23,963	23,068
Unearned Premiums	6,423	6,361	6,322
Premiums Earned	12,066	11,838	11,644
Net Investment Income	1,391	1,482	1,562
Insurance Losses	6,520	7,507	7,407
Amortization of Deferred Policy Acquisition Costs	2,454	2,411	2,330
Other Insurance Operating Costs and Expenses	1,417	1,372	1,333
Premiums Written	12,224	11,870	11,758
Personal insurance [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs	505	477	466
Unpaid Losses	2,235	2,493	2,241
Unearned Premiums	2,216	2,133	2,048
Premiums Earned	4,214	4,024	3,917
Net Investment Income
Insurance Losses	2,224	2,417	2,508
Amortization of Deferred Policy Acquisition Costs	982	942	900
Other Insurance Operating Costs and Expenses	465	458	436
Premiums Written	4,322	4,125	3,977
Commercial insurance [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs	493	477	475
Unpaid Losses	13,147	13,288	12,422
Unearned Premiums	2,792	2,794	2,746
Premiums Earned	5,237	5,144	4,945
Net Investment Income
Insurance Losses	2,891	3,512	3,366
Amortization of Deferred Policy Acquisition Costs	970	970	929
Other Insurance Operating Costs and Expenses	665	620	617
Premiums Written	5,273	5,174	5,051
Specialty insurance [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs	257	252	269
Unpaid Losses	7,307	7,622	7,677
Unearned Premiums	1,412	1,429	1,519
Premiums Earned	2,618	2,666	2,769
Net Investment Income
Insurance Losses	1,417	1,622	1,558
Amortization of Deferred Policy Acquisition Costs	502	499	501
Other Insurance Operating Costs and Expenses	287	293	278
Premiums Written	2,633	2,568	2,720
Reinsurance Assumed [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs
Unpaid Losses	457	560	728
Unearned Premiums	3	5	9
Premiums Earned	(3)	4	13
Net Investment Income
Insurance Losses	(12)	(44)	(25)
Amortization of Deferred Policy Acquisition Costs
Other Insurance Operating Costs and Expenses		1	2
Premiums Written	(4)	3	10
Investments [Member]
Supplemental Information for Property, Casualty Insurance Underwriters [Line Items]
Deferred Policy Acquisition Costs
Unpaid Losses
Unearned Premiums
Premiums Earned
Net Investment Income	1,391	1,482	1,562
Insurance Losses
Amortization of Deferred Policy Acquisition Costs
Other Insurance Operating Costs and Expenses
Premiums Written