Finance Receivables - Finance Receivables Summary (Details) - Automobile Loan [Member] - Retail Finance Receivables [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts Notes And Loans Receivable Rollforward [Roll Forward]
Balance at beginning of period	$ 26,400	$ 22,397	$ 18,859
Purchases	19,920	14,468	13,919
Principal collections and other	(12,428)	(9,508)	(7,891)
Charge-offs	(1,171)	(1,136)	(966)
Foreign currency translation	81	179	(1,524)
Balance at end of period	$ 32,802	$ 26,400	$ 22,397