Reinsurance and Indemnification - Effects of reinsurance on property and casualty premiums (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property and casualty insurance premiums earned
Direct	$ 45,822	$ 39,208	$ 38,249
Assumed	199	113	108
Ceded	(1,982)	(1,154)	(1,136)
Net amount	44,039	38,167	37,221
Property and casualty insurance premiums
Property and casualty insurance premiums written
Direct	45,523	38,695	37,976
Assumed	213	105	95
Ceded	(1,736)	(1,142)	(1,117)
Property and casualty insurance premiums written, net of recoverables	44,000	37,658	36,954
Property and casualty insurance premiums earned
Direct	43,944	38,115	37,104
Assumed	178	99	94
Ceded	(1,904)	(1,141)	(1,122)
Net amount	42,218	37,073	36,076
Accident and health insurance
Property and casualty insurance premiums earned
Direct	1,722	931	994
Assumed	6	0	0
Ceded	(72)	(5)	(6)
Net amount	1,656	926	988
Accident and health insurance premiums and contract charges
Direct	1,878	1,093	1,145
Assumed	21	14	14
Ceded	(78)	(13)	(14)
Accident and health insurance premiums and contract charges, net of recoverables	$ 1,821	$ 1,094	$ 1,145