Finance Receivables - Aging Analysis (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 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	$ 121,536	$ 116,600	$ 107,092
Consumer Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	23	24
Finance Receivables Aging Analysis [Abstract]
Total past due	826	934
Current	75,543	74,253
Financing Receivables	76,369	75,187	66,460
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	95	122
Current	45,072	41,291
Financing Receivables	45,167	41,413	$ 40,632
31-60 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	667	748
61-90 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	85	113
91-120 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	33	36
Greater Than 120 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	$ 41	$ 37