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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Property-liability insurance claims and claims expense
Beginning balance			$ 39,858
Incurred claims and claims expense related to:
Prior years	$ 32	$ 183	(322)	$ 380
Claims and claims expense paid related to:
Ending balance	42,743		42,743
Property and casualty
Property-liability insurance claims and claims expense
Beginning balance			39,858	37,541
Less recoverables	8,728	8,654	8,728	8,654	$ 8,396	$ 9,176
Activity in the reserve for property-liability insurance claims and claims expense:
Net beginning balance			31,462	28,365
Incurred claims and claims expense related to:
Current year			31,033	31,910
Prior years			(322)	380
Total incurred			30,711	32,290
Claims and claims expense paid related to:
Current year			(15,977)	(16,593)
Prior years			(12,181)	(12,057)
Total paid			(28,158)	(28,650)
Net ending balance	34,015	32,005	34,015	32,005
Plus: Recoverables	8,728	8,654	8,728	8,654	$ 8,396	$ 9,176
Ending balance	$ 42,743	$ 40,659	$ 42,743	$ 40,659