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	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Incurred claims and claims expense related to:
Prior years	$ (241)	$ 8
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	6,284	5,333
Prior years	(241)	8
Total incurred	6,043	5,341
Claims and claims expense paid related to:
Current year	(2,541)	(2,352)
Prior years	(3,731)	(3,554)
Total paid	(6,272)	(5,906)
Net balance as of March 31	22,145	20,235
Plus recoverables	9,269	6,913
Balance as of March 31	$ 31,414	$ 27,148