Reserve for Property and Casualty Insurance Claims and Claims Expense - Schedule of Rollforward of Reserve for Property and Casualty Insurance Claims and Claims Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Activity in the reserve for property-liability insurance claims and claims expense:
Beginning balance	$ 39,858
Incurred claims and claims expense related to:
Prior years	(308)	$ 549	$ 1,741
Total incurred	2,900	2,800	2,650
Claims and claims expense paid related to:
Ending balance	41,917	39,858
Property and casualty
Activity in the reserve for property-liability insurance claims and claims expense:
Beginning balance	39,858	37,541	33,060
Less recoverables	(8,396)	(9,176)	(9,479)
Net balance, beginning	31,462	28,365	23,581
Incurred claims and claims expense related to:
Current year	40,043	40,521	35,523
Prior years	(308)	549	1,741
Total incurred	39,735	41,070	37,264
Claims and claims expense paid related to:
Current year	(23,488)	(23,607)	(20,739)
Prior years	(14,394)	(14,366)	(11,741)
Total paid	(37,882)	(37,973)	(32,480)
Net balance, ending	33,315	31,462	28,365
Plus recoverables	(8,602)	(8,396)	(9,176)
Ending balance	$ 41,917	$ 39,858	$ 37,541