Reserve for Property-Liability Insurance Claims and Claims Expense (Details) - Property-Liability - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 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	5,513	5,660
Prior years	(97)	24
Total incurred	5,416	5,684
Claims and claims expense paid related to:
Current year	2,239	2,148
Prior years	2,815	2,867
Total paid	5,054	5,015
Net balance as of March 31	19,445	18,646
Plus reinsurance recoverables	6,183	5,959
Balance as of March 31	25,628	24,605
SquareTrade
Activity in the reserve for property-liability insurance claims and claims expense:
Net balance as of January 1	$ 17	$ 0