Reserve for Property-Liability Insurance Claims and Claims Expense (Details) - Property-Liability - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
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	11,291	11,564
Prior years	(186)	21
Total incurred	11,105	11,585
Claims and claims expense paid related to:
Current year	6,060	6,138
Prior years	4,450	4,553
Total paid	10,510	10,691
Net balance as of June 30	19,678	18,871
Plus reinsurance recoverables	6,206	6,033
Balance as of June 30	25,884	24,904
SquareTrade
Activity in the reserve for property-liability insurance claims and claims expense:
Net balance as of January 1	$ 17	$ 0