Schedule III (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule III
Deferred acquisition costs	$ 1,792	$ 1,786	$ 1,782
Claims and claim adjustment expense reserves	50,922	51,392	51,581
Unearned premiums	11,241	11,102	10,921
Earned premiums	22,357	22,090	21,432
Net investment income	2,889	2,879	3,059
Claims and claim adjustment expenses	14,676	16,276	13,210
Amortization of deferred acquisition costs	3,910	3,876	3,802
Other operating expenses	3,988	3,942	3,794
Net written premiums	22,447	22,187	21,635
Total reportable segments [Member]
Schedule III
Deferred acquisition costs	1,792	1,786	1,782
Claims and claim adjustment expense reserves	50,888	51,353	51,537
Unearned premiums	11,241	11,102	10,921
Earned premiums	22,357	22,090	21,432
Net investment income	2,889	2,879	3,059
Claims and claim adjustment expenses	14,676	16,276	13,210
Amortization of deferred acquisition costs	3,910	3,876	3,802
Other operating expenses	3,587	3,500	3,379
Net written premiums	22,447	22,187	21,635
Business Insurance [Member]
Schedule III
Deferred acquisition costs	843	816	806
Claims and claim adjustment expense reserves	39,598	40,129	40,318
Unearned premiums	5,728	5,482	5,364
Earned premiums	11,691	11,327	10,766
Net investment income	2,090	2,041	2,156
Claims and claim adjustment expenses	7,857	8,447	6,504
Amortization of deferred acquisition costs	1,884	1,815	1,749
Other operating expenses	2,020	1,944	1,904
Net written premiums	11,872	11,340	10,857
Financial, Professional & International Insurance [Member]
Schedule III
Deferred acquisition costs	325	332	352
Claims and claim adjustment expense reserves	6,445	6,857	6,999
Unearned premiums	1,964	2,043	2,139
Earned premiums	3,045	3,174	3,317
Net investment income	395	414	439
Claims and claim adjustment expenses	1,314	1,487	1,700
Amortization of deferred acquisition costs	589	603	612
Other operating expenses	667	648	608
Net written premiums	2,981	3,102	3,211
Personal Insurance [Member]
Schedule III
Deferred acquisition costs	624	638	624
Claims and claim adjustment expense reserves	4,845	4,367	4,220
Unearned premiums	3,549	3,577	3,418
Earned premiums	7,621	7,589	7,349
Net investment income	404	424	464
Claims and claim adjustment expenses	5,505	6,342	5,006
Amortization of deferred acquisition costs	1,437	1,458	1,441
Other operating expenses	900	908	867
Net written premiums	7,594	7,745	7,567
Other [Member]
Schedule III
Claims and claim adjustment expense reserves	34	39	44
Other operating expenses	$ 401	$ 442	$ 415