Consolidated Supplementary Insurance Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Supplementary Insurance Information Schedule [Abstract]
Deferred Policy Acquisition Costs	$ 1,630	$ 1,562	$ 1,533
Unpaid Losses	23,068	22,718	22,839
Unearned Premiums	6,322	6,189	6,153
Premiums Earned	11,644	11,215	11,331
Net Investment Income	1,562	1,558	1,549
Insurance Losses	7,407	6,499	6,268
Amortization of Deferred Policy Acquisition Costs	3,225	3,067	3,021
Other Insurance Operating Costs and Expenses	438	427	411
Premiums Written	11,758	11,236	11,077
Personal insurance [Member]
Consolidated Supplementary Insurance Information Schedule [Abstract]
Deferred Policy Acquisition Costs	606	563	537
Unpaid Losses	2,241	2,144	2,133
Unearned Premiums	2,048	1,995	1,929
Premiums Earned	3,917	3,768	3,692
Insurance Losses	2,508	2,210	1,923
Amortization of Deferred Policy Acquisition Costs	1,196	1,116	1,064
Other Insurance Operating Costs and Expenses	125	113	101
Premiums Written	3,977	3,825	3,657
Commercial insurance [Member]
Consolidated Supplementary Insurance Information Schedule [Abstract]
Deferred Policy Acquisition Costs	661	636	628
Unpaid Losses	12,422	11,807	11,531
Unearned Premiums	2,746	2,630	2,583
Premiums Earned	4,945	4,647	4,762
Insurance Losses	3,366	2,807	2,773
Amortization of Deferred Policy Acquisition Costs	1,336	1,268	1,290
Other Insurance Operating Costs and Expenses	219	216	214
Premiums Written	5,051	4,676	4,660
Specialty insurance [Member]
Consolidated Supplementary Insurance Information Schedule [Abstract]
Deferred Policy Acquisition Costs	362	361	364
Unpaid Losses	7,677	7,872	8,071
Unearned Premiums	1,519	1,549	1,614
Premiums Earned	2,769	2,787	2,829
Insurance Losses	1,558	1,503	1,606
Amortization of Deferred Policy Acquisition Costs	691	677	651
Other Insurance Operating Costs and Expenses	93	98	95
Premiums Written	2,720	2,727	2,739
Reinsurance Assumed [Member]
Consolidated Supplementary Insurance Information Schedule [Abstract]
Deferred Policy Acquisition Costs	1	2	4
Unpaid Losses	728	895	1,104
Unearned Premiums	9	15	27
Premiums Earned	13	13	48
Insurance Losses	(25)	(21)	(34)
Amortization of Deferred Policy Acquisition Costs	2	6	16
Other Insurance Operating Costs and Expenses	1	0	1
Premiums Written	10	8	21
Investments [Member]
Consolidated Supplementary Insurance Information Schedule [Abstract]
Net Investment Income	$ 1,562	$ 1,558	$ 1,549