Variable Interest Entities - Assets and liabilities of consolidated VIEs (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Investments
Fixed income securities, at fair value	$ 39,989	$ 42,565
Short-term investments, at fair value	6,428	6,807
Deferred policy acquisition costs	4,600	3,774
Premium installment receivables, net	8,406	6,463
Reinsurance and indemnification recoverables, net	10,442	7,215
Other assets, net	5,966	2,756
Total assets	133,440	125,987
Liabilities
Reserve for property and casualty insurance claims and claims expense	33,286	27,610
Unearned premiums	19,627	15,946
Total liabilities	106,733	$ 95,770
Variable Interest Entity, Primary Beneficiary
Investments
Fixed income securities, at fair value	330
Short-term investments, at fair value	47
Deferred policy acquisition costs	15
Premium installment receivables, net	43
Reinsurance and indemnification recoverables, net	117
Other assets, net	124
Total assets	676
Liabilities
Reserve for property and casualty insurance claims and claims expense	238
Unearned premiums	194
Other liabilities and expenses	273
Total liabilities	$ 705