Schedule III (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule III
Deferred acquisition costs	$ 1,786	$ 1,782	$ 1,758
Claims and claim adjustment expense reserves	51,419	51,606	53,602
Unearned premiums	11,102	10,921	10,861
Earned premiums	22,090	21,432	21,418
Net investment income	2,879	3,059	2,776
Claims and claim adjustment expenses	16,276	13,210	12,408
Amortization of deferred acquisition costs	3,876	3,802	3,813
Other operating expenses	3,942	3,794	3,748
Net written premiums	22,187	21,635	21,336
Total reportable segments [Member]
Schedule III
Deferred acquisition costs	1,786	1,782	1,758
Claims and claim adjustment expense reserves	51,353	51,537	53,529
Unearned premiums	11,102	10,921	10,861
Earned premiums	22,090	21,432	21,418
Net investment income	2,879	3,059	2,776
Claims and claim adjustment expenses	16,276	13,210	12,408
Amortization of deferred acquisition costs	3,876	3,802	3,813
Other operating expenses	3,500	3,379	3,329
Net written premiums	22,187	21,635	21,336
Business Insurance [Member]
Schedule III
Deferred acquisition costs	816	806	791
Claims and claim adjustment expense reserves	40,129	40,318	42,103
Unearned premiums	5,482	5,364	5,380
Earned premiums	11,327	10,766	10,968
Net investment income	2,041	2,156	1,902
Claims and claim adjustment expenses	8,447	6,504	6,037
Amortization of deferred acquisition costs	1,815	1,749	1,775
Other operating expenses	1,944	1,904	1,966
Net written premiums	11,340	10,857	10,902
Financial, Professional & International Insurance [Member]
Schedule III
Deferred acquisition costs	332	352	369
Claims and claim adjustment expense reserves	6,857	6,999	7,197
Unearned premiums	2,043	2,139	2,276
Earned premiums	3,174	3,317	3,333
Net investment income	414	439	452
Claims and claim adjustment expenses	1,487	1,700	1,747
Amortization of deferred acquisition costs	603	612	622
Other operating expenses	648	608	579
Net written premiums	3,102	3,211	3,285
Personal Insurance [Member]
Schedule III
Deferred acquisition costs	638	624	598
Claims and claim adjustment expense reserves	4,367	4,220	4,229
Unearned premiums	3,577	3,418	3,205
Earned premiums	7,589	7,349	7,117
Net investment income	424	464	422
Claims and claim adjustment expenses	6,342	5,006	4,624
Amortization of deferred acquisition costs	1,458	1,441	1,416
Other operating expenses	908	867	784
Net written premiums	7,745	7,567	7,149
Other [Member]
Schedule III
Claims and claim adjustment expense reserves	66	69	73
Other operating expenses	$ 442	$ 415	$ 419