Finance Receivables - Finance Receivables, net (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables, net	$ 42,172	$ 33,475
Fair value of finance receivables	42,178	33,528
Commercial Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total finance receivables	10,312	7,880	$ 5,392	$ 4,884
Automobile Loan [Member] | Retail Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables, collectively evaluated for impairment, net of fees	30,574	24,480
Finance receivables, individually evaluated for impairment, net of fees	2,228	1,920
Total finance receivables	32,802	26,400	$ 22,397	$ 18,859
Less: allowance for loan losses - collective	(561)	(489)
Less: allowance for loan losses - specific	(328)	(276)
Total finance receivables, net	31,913	25,635
Deferred income	228	178
Automobile Loan [Member] | Commercial Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Finance receivables, collectively evaluated for impairment, net of fees	10,290	7,853
Finance receivables, individually evaluated for impairment, net of fees	22	27
Total finance receivables	10,312	7,880
Less: allowance for loan losses - collective	(50)	(36)
Less: allowance for loan losses - specific	(3)	(4)
Total finance receivables, net	$ 10,259	$ 7,840