Schedule III (details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule III
Deferred acquisition costs	$ 1,849	$ 1,835	$ 1,804
Claims and claim adjustment expense reserves	48,295	49,850	50,895
Unearned premiums	11,971	11,839	11,850
Earned premiums	23,874	23,713	22,637
Net investment income	2,379	2,787	2,716
Claims and claim adjustment expenses	13,723	13,870	13,307
Amortization of deferred acquisition costs	3,885	3,882	3,821
Other operating expenses	4,452	4,321	4,118
Net written premiums	24,121	23,904	22,767
Business and International Insurance [Member]
Schedule III
Net written premiums	14,583	14,636	13,512
Bond & Specialty Insurance [Member]
Schedule III
Net written premiums	2,081	2,103	2,030
Personal Insurance [Member]
Schedule III
Net written premiums	7,457	7,165	7,225
Reportable Segments [Member]
Schedule III
Deferred acquisition costs	1,849	1,835	1,804
Claims and claim adjustment expense reserves	48,272	49,824	50,865
Unearned premiums	11,971	11,839	11,850
Earned premiums	23,874	23,713	22,637
Net investment income	2,379	2,787	2,716
Claims and claim adjustment expenses	13,723	13,870	13,307
Amortization of deferred acquisition costs	3,885	3,882	3,821
Other operating expenses	4,048	3,921	3,737
Net written premiums	24,121	23,904	22,767
Reportable Segments [Member] | Business and International Insurance [Member]
Schedule III
Deferred acquisition costs	1,072	1,080	1,046
Claims and claim adjustment expense reserves	41,563	42,700	43,181
Unearned premiums	7,147	7,208	7,170
Earned premiums	14,521	14,512	13,332
Net investment income	1,824	2,156	2,087
Claims and claim adjustment expenses	8,859	9,145	8,285
Amortization of deferred acquisition costs	2,329	2,321	2,158
Other operating expenses	2,686	2,541	2,369
Net written premiums	14,583	14,636	13,512
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Schedule III
Deferred acquisition costs	225	222	213
Claims and claim adjustment expense reserves	3,157	3,435	3,921
Unearned premiums	1,292	1,286	1,264
Earned premiums	2,085	2,076	1,981
Net investment income	223	252	260
Claims and claim adjustment expenses	643	481	695
Amortization of deferred acquisition costs	393	388	378
Other operating expenses	389	403	388
Net written premiums	2,081	2,103	2,030
Reportable Segments [Member] | Personal Insurance [Member]
Schedule III
Deferred acquisition costs	552	533	545
Claims and claim adjustment expense reserves	3,552	3,689	3,763
Unearned premiums	3,532	3,345	3,416
Earned premiums	7,268	7,125	7,324
Net investment income	332	379	369
Claims and claim adjustment expenses	4,221	4,244	4,327
Amortization of deferred acquisition costs	1,163	1,173	1,285
Other operating expenses	973	977	980
Net written premiums	7,457	7,165	7,225
Other [Member]
Schedule III
Claims and claim adjustment expense reserves	23	26	30
Other operating expenses	$ 404	$ 400	$ 381