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		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 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	$ (203)	$ 212	(354)	$ 197
Claims and claims expense paid related to:
Ending balance	41,553		41,553
Property and casualty
Property-liability insurance claims and claims expense
Beginning balance			39,858	37,541
Less recoverables	8,341	8,730	8,341	8,730	$ 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			20,656	21,856
Prior years			(354)	197
Total incurred			20,302	22,053
Claims and claims expense paid related to:
Current year			(9,087)	(9,094)
Prior years			(9,465)	(9,523)
Total paid			(18,552)	(18,617)
Net ending balance	33,212	31,801	33,212	31,801
Plus: Recoverables	8,341	8,730	8,341	8,730	$ 8,396	$ 9,176
Ending balance	$ 41,553	$ 40,531	$ 41,553	$ 40,531