Finance Receivables - Delinquency (Details) - Retail Finance Receivables [Member] - Automobile Loan [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
In repossession	$ 51	$ 48
In repossession (percent)	0.10%	0.20%
Financing receivable and in repossession past due	$ 1,498	$ 1,432
Financing receivable and in repossession past due (percent)	4.10%	4.70%
31 to 60 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable past due	$ 1,006	$ 963
Financing receivable past due (percent)	2.80%	3.10%
Greater Than 60 Days [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable past due	$ 441	$ 421
Financing receivable past due (percent)	1.20%	1.40%
Thirty or More Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Financing receivable past due	$ 1,447	$ 1,384
Financing receivable past due (percent)	4.00%	4.50%