Finance Receivables - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Retail Finance Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrual of finance charge income	$ 847	$ 778

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant