TRANSFERS OF FINANCIAL ASSETS - Cash Proceeds (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Transfers and Servicing [Abstract]
Collections reinvested in revolving receivables	$ 0	$ 6,051	$ 0	$ 11,732
Interests in conduits 1	$ 211	$ 1,363	$ 656	$ 1,914

Cash Flows between a transferor and a transferee attributable to collections reinvested in revolving period transfers related to either a securitization, asset-backed financing arrangement, or similar transfer in which the transferor has continuing involvement with the transferred financial assets underlying the transaction (including, but not limited to, servicing, recourse, and restrictions on transferor's interests in the transferred financial assets).

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph d
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107207-111719

Name:	us-gaap_CashFlowsBetweenTransfereeAndTransferorProceedsFromCollectionsReinvestedInRevolvingPeriodTransfers
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration