Reserve for Property and Casualty Insurance Claims and Claims Expense - Rollforward of the reserve for property and casualty insurance claims and claims expense (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Incurred claims and claims expense related to:
Prior years	$ (226)	$ (3)
National General
Activity in the reserve for property-liability insurance claims and claims expense:
National General acquisition as of January 4, 2021	1,797	0
Property-Liability
Activity in the reserve for property-liability insurance claims and claims expense:
Balance as of January 1	27,610	27,712
Less recoverables	(7,033)	(6,912)
Net balance as of January 1	20,577	20,800
Incurred claims and claims expense related to:
Current year	13,476	10,566
Prior years	(226)	(3)
Total incurred	13,250	10,563
Claims and claims expense paid related to:
Current year	(6,919)	(5,777)
Prior years	(6,134)	(5,173)
Total paid	(13,053)	(10,950)
Net balance as of June 30	22,571	20,413
Plus recoverables	9,066	7,013
Balance as of June 30	$ 31,637	$ 27,426