Reserve for Property and Casualty Insurance Claims and Claims Expense - Schedule of Rollforward of the Reserve for Property and Casualty Insurance Claims and Claims Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021
Incurred claims and claims expense related to:
Prior years	$ 183	$ 866	$ 380	$ 1,470
Property and casualty
Property-liability insurance claims and claims expense
Beginning balance			37,541	33,060
Less recoverables	8,654	9,556	8,654	9,556	$ 9,176	$ 9,479
Activity in the reserve for property-liability insurance claims and claims expense:
Net beginning balance			28,365	23,581
Incurred claims and claims expense related to:
Current year			31,910	25,792
Prior years			380	1,470
Total incurred			32,290	27,262
Claims and claims expense paid related to:
Current year			(16,593)	(14,020)
Prior years			(12,057)	(9,850)
Total paid			(28,650)	(23,870)
Net ending balance	32,005	26,973	32,005	26,973
Plus recoverables	8,654	9,556	8,654	9,556	$ 9,176	$ 9,479
Ending balance	$ 40,659	$ 36,529	$ 40,659	$ 36,529