Reserve for Property and Liability 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, 2019	Jun. 30, 2018
Incurred claims and claims expense related to:
Prior years	$ (74)
Property-Liability
Activity in the reserve for property-liability insurance claims and claims expense:
Balance as of January 1	27,423	$ 26,325
Less recoverables	(7,155)	(6,471)
Net balance as of January 1	20,268	19,854
Incurred claims and claims expense related to:
Current year	12,250	11,054
Prior years	(74)	(148)
Total incurred	12,176	10,906
Claims and claims expense paid related to:
Current year	(6,125)	(5,835)
Prior years	(5,237)	(4,809)
Total paid	(11,362)	(10,644)
Net balance as of June 30	21,082	20,116
Plus recoverables	7,023	6,507
Balance as of June 30	$ 28,105	$ 26,623