Financial Services Finance Receivables - Impaired receivables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable Impaired [Line Items]
Threshold Period for Impaired Finance Receivables	120 days
Consumer [Member]
Financing Receivable Impaired [Line Items]
Recorded investment of receivables that were impaired	$ 386	$ 367
Percentage of recorded investment of receivables that were impaired	0.50%	0.60%
Non-consumer [Member]
Financing Receivable Impaired [Line Items]
Recorded investment of receivables that were impaired	$ 138	$ 107
Percentage of recorded investment of receivables that were impaired	0.40%	0.30%