EMPLOYEE BENEFIT PLANS - EMPLOYEE INCENTIVE-PAY PLANS (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($) $ / Quarter	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Retirement Benefits [Abstract]
Operational Performance Rewards Program entitles all Air Group employees to maximum quarterly payouts (in dollars per quarter) \| $ / Quarter	300
Variable incentive pay \| $	$ 147	$ 135	$ 127

Amount of labor-related expenses classified as other.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.4)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

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