Finance Receivables - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable, Gross, Allowance, and Net [Abstract]
Accrual of finance charge income	$ 807	$ 778
TDR's - subsequent default	$ 26	$ 20	$ 25