Schedule III (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Schedule III
Deferred acquisition costs	$ 2,836	$ 2,542	$ 2,358
Claims and claim adjustment expense reserves	58,649	56,907	54,521
Unearned premiums	18,240	16,469	15,222
Earned premiums	33,763	30,855	29,044
Net investment income	2,562	3,033	2,227
Claims and claim adjustment expenses	22,854	20,298	19,123
Amortization of deferred acquisition costs	5,515	5,043	4,773
Other operating expenses	5,161	5,017	4,848
Net written premiums	35,414	31,959	29,732
Reportable segments [Member]
Schedule III
Deferred acquisition costs	2,836	2,542	2,358
Claims and claim adjustment expense reserves	58,643	56,897	54,510
Unearned premiums	18,240	16,469	15,222
Earned premiums	33,763	30,855	29,044
Net investment income	2,562	3,033	2,227
Claims and claim adjustment expenses	22,854	20,298	19,123
Amortization of deferred acquisition costs	5,515	5,043	4,773
Other operating expenses	4,779	4,648	4,478
Net written premiums	35,414	31,959	29,732
Reportable segments [Member] | Business Insurance [Member]
Schedule III
Deferred acquisition costs	1,315	1,206	1,152
Claims and claim adjustment expense reserves	45,909	45,358	44,162
Unearned premiums	8,619	7,953	7,556
Earned premiums	17,095	15,734	15,294
Net investment income	1,864	2,265	1,633
Claims and claim adjustment expenses	10,907	10,398	10,804
Amortization of deferred acquisition costs	2,788	2,581	2,518
Other operating expenses	2,827	2,746	2,664
Net written premiums	17,635	16,092	15,431
Reportable segments [Member] | Bond & Specialty Insurance [Member]
Schedule III
Deferred acquisition costs	430	375	328
Claims and claim adjustment expense reserves	4,482	4,247	3,814
Unearned premiums	2,679	2,360	2,020
Earned premiums	3,418	3,138	2,823
Net investment income	258	247	213
Claims and claim adjustment expenses	1,378	1,473	1,464
Amortization of deferred acquisition costs	625	570	519
Other operating expenses	590	532	500
Net written premiums	3,732	3,376	2,951
Reportable segments [Member] | Personal Insurance [Member]
Schedule III
Deferred acquisition costs	1,091	961	878
Claims and claim adjustment expense reserves	8,252	7,292	6,534
Unearned premiums	6,942	6,156	5,646
Earned premiums	13,250	11,983	10,927
Net investment income	440	521	381
Claims and claim adjustment expenses	10,569	8,427	6,855
Amortization of deferred acquisition costs	2,102	1,892	1,736
Other operating expenses	1,362	1,370	1,314
Net written premiums	14,047	12,491	11,350
Other [Member]
Schedule III
Deferred acquisition costs	0	0	0
Claims and claim adjustment expense reserves	6	10	11
Unearned premiums	0	0	0
Earned premiums	0	0	0
Net investment income	0	0	0
Claims and claim adjustment expenses	0	0	0
Amortization of deferred acquisition costs	0	0	0
Other operating expenses	382	369	370
Net written premiums	$ 0	$ 0	$ 0