Variable Interest Entities - Schedule of Assets and Liabilities of Reciprocal Exchanges (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Investments
Fixed income securities	$ 48,865	$ 42,485
Short-term investments	5,144	4,173
Deferred policy acquisition costs	5,940	5,442	$ 4,738	$ 3,776
Premium installment and other receivables, net	10,044	9,165
Reinsurance recoverables, net	8,809	9,619
Other assets	6,051	5,904
Total assets	103,362	97,989
Liabilities
Reserve for property and casualty insurance claims and claims expense	39,858	37,541
Unearned premiums	24,709	22,299
Total liabilities	85,732	80,626
Variable Interest Entity, Primary Beneficiary
Investments
Fixed income securities	267	302
Short-term investments	7	13
Deferred policy acquisition costs	20	15
Premium installment and other receivables, net	40	43
Reinsurance recoverables, net	111	97
Other assets	54	90
Total assets	499	560
Liabilities
Reserve for property and casualty insurance claims and claims expense	201	209
Unearned premiums	147	171
Other liabilities and accrued expenses	296	311
Total liabilities	$ 644	$ 691