Reinsurance and Indemnification - Effects of reinsurance on property and casualty premiums (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property and casualty insurance premiums earned
Direct	$ 39,178	$ 36,978	$ 35,115
Assumed	806	841	837
Ceded	(1,407)	(1,306)	(1,274)
Net amount	38,577	36,513	34,678
Property-liability insurance premiums earned
Property and casualty insurance premiums written
Direct	37,976	35,895	33,685
Assumed	95	99	64
Ceded	(1,117)	(1,008)	(1,007)
Property and casualty insurance premiums written, net of recoverables	36,954	34,986	32,742
Property and casualty insurance premiums earned
Direct	37,104	34,977	33,221
Assumed	94	87	50
Ceded	(1,122)	(1,016)	(971)
Net amount	36,076	34,048	32,300
Life and annuity premiums and contract charges
Life premiums and contract charges
Direct	2,074	2,001	1,894
Assumed	712	754	787
Ceded	(285)	(290)	(303)
Life premiums and contract charges, net of recoverables	$ 2,501	$ 2,465	$ 2,378