Reinsurance and Indemnification - Schedule of Effects of Reinsurance and Indemnification on Property and Casualty Premiums Written and Earned and Accident and Health Insurance Premiums and Contract Charges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property and casualty insurance premiums earned
Direct	$ 54,166	$ 49,390	$ 45,836
Assumed	386	252	199
Ceded	(2,036)	(1,906)	(1,983)
Net amount	52,516	47,736	44,052
Property and casualty insurance premiums
Property and casualty insurance premiums written
Direct	54,632	50,065	45,523
Assumed	396	245	213
Ceded	(2,018)	(1,824)	(1,736)
Property and casualty insurance premiums written, net of recoverables	53,010	48,486	44,000
Property and casualty insurance premiums earned
Direct	52,301	47,552	43,944
Assumed	358	221	178
Ceded	(1,989)	(1,869)	(1,904)
Net amount	50,670	45,904	42,218
Accident and health insurance
Property and casualty insurance premiums earned
Direct	1,639	1,624	1,732
Assumed	12	14	6
Ceded	(41)	(31)	(72)
Net amount	1,610	1,607	1,666
Accident and health insurance premiums and contract charges
Direct	1,865	1,838	1,892
Assumed	28	31	21
Ceded	(47)	(37)	(79)
Accident and health insurance premiums and contract charges, net of recoverables	$ 1,846	$ 1,832	$ 1,834