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, 2024	Dec. 31, 2023	Dec. 31, 2022
Property and casualty insurance premiums earned
Direct	$ 60,166	$ 54,166	$ 49,390
Assumed	403	386	252
Ceded	(2,260)	(2,036)	(1,906)
Net amount	58,309	52,516	47,736
Property and casualty insurance premiums
Property and casualty insurance premiums written
Direct	60,574	54,632	50,065
Assumed	352	396	245
Ceded	(2,203)	(2,018)	(1,824)
Property and casualty insurance premiums written, net of recoverables	58,723	53,010	48,486
Property and casualty insurance premiums earned
Direct	58,221	52,301	47,552
Assumed	377	358	221
Ceded	(2,210)	(1,989)	(1,869)
Net amount	56,388	50,670	45,904
Accident and health insurance
Property and casualty insurance premiums earned
Direct	1,687	1,639	1,624
Assumed	10	12	14
Ceded	(45)	(41)	(31)
Net amount	1,652	1,610	1,607
Accident and health insurance premiums and contract charges
Direct	1,945	1,865	1,838
Assumed	26	28	31
Ceded	(50)	(47)	(37)
Accident and health insurance premiums and contract charges, net of recoverables	$ 1,921	$ 1,846	$ 1,832