EMPLOYEE BENEFIT PLANS - EMPLOYEE INCENTIVE-PAY PLANS (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / Quarter	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Variable incentive pay | $	$ 135	$ 127	$ 120
Operational Performance Rewards Program entitles all Air Group employees to maximum quarterly payouts (in dollars per quarter) | $ / Quarter	300