Schedule III (details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule III
Deferred acquisition costs	$ 1,835	$ 1,804	$ 1,792
Claims and claim adjustment expense reserves	49,850	50,895	50,922
Unearned premiums	11,839	11,850	11,241
Earned premiums	23,713	22,637	22,357
Net investment income	2,787	2,716	2,889
Claims and claim adjustment expenses	13,870	13,307	14,676
Amortization of deferred acquisition costs	3,882	3,821	3,910
Other operating expenses	4,321	4,118	3,988
Net written premiums	23,904	22,767	22,447
Reportable Segments [Member]
Schedule III
Deferred acquisition costs	1,835	1,804	1,792
Claims and claim adjustment expense reserves	49,824	50,865	50,888
Unearned premiums	11,839	11,850	11,241
Earned premiums	23,713	22,637	22,357
Net investment income	2,787	2,716	2,889
Claims and claim adjustment expenses	13,870	13,307	14,676
Amortization of deferred acquisition costs	3,882	3,821	3,910
Other operating expenses	3,921	3,737	3,587
Net written premiums	23,904	22,767	22,447
Reportable Segments [Member] | Business and International Insurance [Member]
Schedule III
Deferred acquisition costs	1,080	1,046	959
Claims and claim adjustment expense reserves	42,700	43,181	41,979
Unearned premiums	7,208	7,170	6,438
Earned premiums	14,512	13,332	12,779
Net investment income	2,156	2,087	2,205
Claims and claim adjustment expenses	9,145	8,285	8,383
Amortization of deferred acquisition costs	2,321	2,158	2,100
Other operating expenses	2,541	2,369	2,304
Net written premiums	14,636	13,512	12,929
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Schedule III
Deferred acquisition costs	222	213	209
Claims and claim adjustment expense reserves	3,435	3,921	4,064
Unearned premiums	1,286	1,264	1,254
Earned premiums	2,076	1,981	1,957
Net investment income	252	260	280
Claims and claim adjustment expenses	481	695	788
Amortization of deferred acquisition costs	388	378	373
Other operating expenses	403	388	383
Net written premiums	2,103	2,030	1,924
Reportable Segments [Member] | Personal Insurance [Member]
Schedule III
Deferred acquisition costs	533	545	624
Claims and claim adjustment expense reserves	3,689	3,763	4,845
Unearned premiums	3,345	3,416	3,549
Earned premiums	7,125	7,324	7,621
Net investment income	379	369	404
Claims and claim adjustment expenses	4,244	4,327	5,505
Amortization of deferred acquisition costs	1,173	1,285	1,437
Other operating expenses	977	980	900
Net written premiums	7,165	7,225	7,594
Other [Member]
Schedule III
Claims and claim adjustment expense reserves	26	30	34
Other operating expenses	$ 400	$ 381	$ 401