Variable Interest Entities - Schedule of Assets and Liabilities of Reciprocal Exchanges (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Investments
Fixed income securities	$ 46,771	$ 42,485
Short-term investments	3,368	4,173
Deferred policy acquisition costs	5,824	5,442	$ 5,291
Premium installment and other receivables, net	10,102	9,165
Reinsurance recoverables, net	9,083	9,619
Other assets	6,196	5,904
Total assets	101,176	97,989
Liabilities
Reserve for property and casualty insurance claims and claims expense	40,659	37,541
Unearned premiums	24,518	22,299
Total liabilities	86,729	80,626
Variable Interest Entity, Primary Beneficiary
Investments
Fixed income securities	262	302
Short-term investments	4	13
Deferred policy acquisition costs	19	15
Premium installment and other receivables, net	42	43
Reinsurance recoverables, net	88	97
Other assets	68	90
Total assets	483	560
Liabilities
Reserve for property and casualty insurance claims and claims expense	191	209
Unearned premiums	148	171
Other liabilities and expenses	294	311
Total liabilities	$ 633	$ 691