Finance Receivables - Aging Analysis (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 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	$ 116,630	$ 116,600	$ 111,172
Uncollected Interest Receivable Excluded From Finance Receivable	241	241
Consumer Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing	21	24
Finance Receivables Aging Analysis [Abstract]
Total past due	882	934
Current	75,945	74,253
Financing Receivables	76,827	75,187	72,456
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	77	122
Current	39,726	41,291
Financing Receivables	39,803	41,413	$ 38,716
31-60 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	691	748
61-90 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	109	113
91-120 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	42	36
Greater Than 120 Days Past Due [Member] | Consumer Segment [Member]
Finance Receivables Aging Analysis [Abstract]
Total past due	$ 40	$ 37