FAIR VALUE MEASUREMENT - Level 3 Fair Value Rollforward Narrative (Details) - Long-term debt - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Fair value, assets and liabilities measured on recurring basis, level 3 fair-value category disclosures
Transfers into Level 3, liabilities	$ 877	$ 940
Transfers out of Level 3, liabilities	$ 1,601	$ 764

Amount of transfers of financial instrument classified as a liability out of level 3 of the fair value hierarchy.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersOutOfLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration