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, 2023	Dec. 31, 2022	Dec. 31, 2021
Incurred claims and claims expense related to:
Prior years	$ 549	$ 1,741	$ 122
Total incurred	41,070	37,264	29,318
Property and casualty
Activity in the reserve for property-liability insurance claims and claims expense:
Beginning balance	37,541	33,060	27,610
Less recoverables	(9,176)	(9,479)	(7,033)
Net balance, beginning	28,365	23,581	20,577
Incurred claims and claims expense related to:
Current year	40,521	35,523	29,196
Prior years	549	1,741	122
Total incurred	41,070
Claims and claims expense paid related to:
Current year	(23,607)	(20,739)	(18,438)
Prior years	(14,366)	(11,741)	(9,807)
Total paid	(37,973)	(32,480)	(28,245)
Net balance, ending	31,462	28,365	23,581
Plus recoverables	(8,396)	(9,176)	(9,479)
Ending balance	39,858	37,541	33,060
Property and casualty | National General Holdings Corp. Acquisitions
Activity in the reserve for property-liability insurance claims and claims expense:
Acquisition balance	0	0	1,797
Property and casualty | SafeAuto acquisition
Activity in the reserve for property-liability insurance claims and claims expense:
Acquisition balance	$ 0	$ 0	$ 134