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	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Incurred claims and claims expense related to:
Prior years	$ (65)	$ (440)
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	21,579	17,075
Prior years	(65)	(440)
Total incurred	21,514	16,635
Claims and claims expense paid related to:
Current year	(12,539)	(9,623)
Prior years	(8,098)	(6,714)
Total paid	(20,637)	(16,337)
Net balance as of September 30	23,251	21,098
Plus recoverables	10,035	6,889
Balance as of September 30	$ 33,286	$ 27,987