Reserve for Property-Liability Insurance Claims and Claims Expense (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Incurred claims and claims expense related to:
Prior years	$ (321)
Property-Liability
Activity in the reserve for property-liability insurance claims and claims expense:
Balance as of January 1	25,250	$ 23,869
Less reinsurance recoverables	6,184	5,892
Net balance as of January 1	19,066	17,977
Incurred claims and claims expense related to:
Current year	16,971	17,018
Prior years	(321)	120
Total incurred	16,650	17,138
Claims and claims expense paid related to:
Current year	10,052	10,210
Prior years	5,784	5,804
Total paid	15,836	16,014
Net balance as of September 30	19,897	19,101
Plus reinsurance recoverables	7,257	6,349
Balance as of September 30	27,154	25,450
SquareTrade | Property-Liability
Activity in the reserve for property-liability insurance claims and claims expense:
SquareTrade acquisition as of January 3, 2017	$ 17	$ 0