Variable Interest Entities - Schedule of Assets and Liabilities of Reciprocal Exchanges (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Investments
Fixed income securities, at fair value	$ 53,961	$ 48,865
Short-term investments	6,994	5,144
Deferred policy acquisition costs	5,751	5,940	$ 5,824
Premium installment and other receivables, net	11,041	10,044
Reinsurance recoverables, net	9,013	8,809
Other assets	5,834	6,051
Total assets	113,743	103,362
Liabilities
Reserve for property and casualty insurance claims and claims expense	42,743	39,858
Unearned premiums	27,059	24,709
Total liabilities	92,905	85,732
Variable Interest Entity, Primary Beneficiary
Investments
Fixed income securities, at fair value	121	267
Short-term investments	96	7
Deferred policy acquisition costs	12	25
Premium installment and other receivables, net	32	44
Reinsurance recoverables, net	68	76
Other assets	10	54
Total assets	339	473
Liabilities
Reserve for property and casualty insurance claims and claims expense	224	201
Unearned premiums	117	177
Other liabilities and expenses	16	77
Total liabilities	357	455
Consolidation, Eliminations
Investments
Total assets	(42)	(26)
Liabilities
Total liabilities	$ (193)	$ (189)