Variable Interest Entities - Schedule of Assets and Liabilities of Reciprocal Exchanges (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
Investments
Fixed income securities, at fair value	$ 50,777	$ 48,865
Short-term investments	4,318	5,144
Deferred policy acquisition costs	5,946	5,940	$ 5,471
Premium installment and other receivables, net	10,573	10,044
Reinsurance recoverables, net	8,726	8,809
Other assets	6,255	6,051
Total assets	105,241	103,362
Liabilities
Reserve for property and casualty insurance claims and claims expense	40,143	39,858
Unearned premiums	24,945	24,709
Total liabilities	86,761	85,732
Variable Interest Entity, Primary Beneficiary
Investments
Fixed income securities, at fair value	241	267
Short-term investments	13	7
Deferred policy acquisition costs	19	25
Premium installment and other receivables, net	38	44
Reinsurance recoverables, net	74	76
Other assets	29	54
Total assets	414	473
Liabilities
Reserve for property and casualty insurance claims and claims expense	227	201
Unearned premiums	160	177
Other liabilities and expenses	41	77
Total liabilities	428	455
Consolidation, Eliminations
Investments
Total assets	(30)	(26)
Liabilities
Total liabilities	$ (201)	$ (189)