Leased Vehicles - Leased Vehicles Summary (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leased Vehicles Accounted For Operating Leases, Net [Roll Forward]
Balance at beginning of period	$ 40,654	$ 22,913	$ 8,238
Leased vehicles purchased	25,421	25,221	20,128
Terminated leases	(11,160)	(4,089)	(1,783)
Leased vehicles returned - default	(627)	(358)	(120)
Manufacturer subvention on leased vehicles purchased	(3,799)	(3,777)	(3,431)
Manufacturer subvention on terminated leases	2,055	678	266
Foreign currency translation	191	66	(385)
Balance at end of period	$ 52,735	$ 40,654	$ 22,913