Variable Interest Entities - Schedule of Assets and Liabilities of Reciprocal Exchanges (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Investments
Fixed income securities	$ 52,747	$ 48,865
Short-term investments	4,537	5,144
Deferred policy acquisition costs	5,773	5,940	$ 5,442	$ 4,738
Premium installment and other receivables, net	10,614	10,044
Reinsurance recoverables, net	8,924	8,809
Other assets	5,140	6,051
Total assets	111,617	103,362
Liabilities
Reserve for property and casualty insurance claims and claims expense	41,917	39,858
Unearned premiums	26,909	24,709
Total liabilities	90,250	85,732
Variable Interest Entity, Primary Beneficiary
Investments
Fixed income securities	47	267
Short-term investments	112	7
Deferred policy acquisition costs	0	20
Premium installment and other receivables, net	9	40
Reinsurance recoverables, net	76	111
Other assets	25	54
Total assets	269	499
Liabilities
Reserve for property and casualty insurance claims and claims expense	214	201
Unearned premiums	22	147
Other liabilities and accrued expenses	235	296
Total liabilities	$ 471	$ 644