Reserve for Property-Liability Insurance Claims and Claims Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Incurred claims and claims expense related to:
Current year	$ 22,238	$ 20,953	$ 19,512
Prior years	17	81	84
Claims and claims expense paid related to:
Balance as of December 31	25,250
Property-Liability
Activity in the reserve for property-liability insurance claims and claims expense:
Balance as of January 1	23,869	22,923	21,857
Less reinsurance recoverables	5,892	5,694	4,664
Net balance as of January 1	17,977	17,229	17,193
Incurred claims and claims expense related to:
Current year	22,238	20,953	19,512
Prior years	(17)	81	(84)
Total incurred	22,221	21,034	19,428
Claims and claims expense paid related to:
Current year	14,222	13,660	12,924
Prior years	6,910	6,626	6,468
Total paid	21,132	20,286	19,392
Net balance as of December 31	19,066	17,977	17,229
Plus reinsurance recoverables	6,184	5,892	5,694
Balance as of December 31	$ 25,250	$ 23,869	$ 22,923