Finance Receivables - Contractual Maturities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Finance Receivables Maturity [Abstract]
Financing Receivable, Gross	$ 121,536	$ 116,600	$ 107,092
Consumer Segment [Member]
Finance Receivables Maturity [Abstract]
Financing Receivable, Gross	76,369	75,187	66,460
Consumer Segment [Member] | Retail [Member]
Finance Receivables Maturity [Abstract]
Financing Receivable, Gross	76,369	75,187
Finance receivables before unearned interest supplements	79,627	78,467
Non-Consumer Segment [Member]
Finance Receivables Maturity [Abstract]
Financing Receivable, Gross	45,167	41,413	$ 40,632
Non-Consumer Segment [Member] | Wholesale and Dealer Loans [Member]
Finance Receivables Maturity [Abstract]
Financing Receivable, Gross	43,230	39,241
Non-Consumer Segment [Member] | Other Finance Receivables [Member]
Finance Receivables Maturity [Abstract]
Financing Receivable, Gross	$ 1,937	$ 2,172