Finance Receivables - Aging Analysis (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold Period For Past Due Finance Receivables	31 days
Finance Receivables Aging Analysis [Abstract]
Financing Receivables	$ 116,480	$ 116,600	$ 108,822
Consumer Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	27	24
Finance Receivables Aging Analysis [Abstract]
Total past due	927	934
Current	74,789	74,253
Financing Receivables	75,716	75,187	68,287
Non-Consumer Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	0	1
Finance Receivables Aging Analysis [Abstract]
Total past due	70	122
Current	40,694	41,291
Financing Receivables	40,764	41,413	$ 40,535
31-60 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	730	748
61-90 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	120	113
91-120 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	37	36
Greater Than 120 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	$ 40	$ 37