LONG-TERM DEBT - LINE OF CREDIT (Details)	3 Months Ended
	Mar. 31, 2020 USD ($) credit_facility	Mar. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Proceeds from Issuance of Secured Debt	$ 825,000,000	$ 254,000,000
Line of Credit Facility, Number of Credit Facilities | credit_facility	3
Line of Credit Facility, Maximum Borrowing Capacity	$ 516,000,000
Line of Credit Facility, Asset Restrictions	500,000,000
Credit Facility 1 [Member] | Secured by aircraft [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	250,000,000
Credit Facility 2 [Member] | Secured by aircraft [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	116,000,000
Credit Facility 3 [Member] | Secured by certain accounts receivable, spare engines, spare parts and ground service equipment [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 150,000,000