Reinsurance and Indemnification - Effects of reinsurance on property and casualty premiums (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property and casualty insurance premiums earned
Direct	$ 40,116	$ 39,178	$ 36,978
Assumed	784	806	841
Ceded	(1,383)	(1,407)	(1,306)
Net amount	39,517	38,577	36,513
Property and casualty insurance premiums
Property and casualty insurance premiums written
Direct	38,695	37,976	35,895
Assumed	105	95	99
Ceded	(1,142)	(1,117)	(1,008)
Property and casualty insurance premiums written, net of recoverables	37,658	36,954	34,986
Property and casualty insurance premiums earned
Direct	38,115	37,104	34,977
Assumed	99	94	87
Ceded	(1,141)	(1,122)	(1,016)
Net amount	37,073	36,076	34,048
Reinsurance ceded
Life premiums and contract charges
Direct	2,001	2,074	2,001
Assumed	685	712	754
Ceded	(242)	(285)	(290)
Life premiums and contract charges, net of recoverables	$ 2,444	$ 2,501	$ 2,465