INCOME TAXES - DEFERRED TAX ASSETS AND LIABILITIES (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Excess of tax over book depreciation	$ 1,312	$ 1,145
Deferred Tax Liabilities, Intangible Assets	17	19
Deferred Tax Liabilities, Other	49	76
Gross deferred tax liabilities	1,734	1,591
Mileage Plan	(436)	(416)
Inventory obsolescence	(21)	(17)
Employee benefits	(145)	(127)
Net operating losses	(28)	(25)
Other - net	(88)	(34)
Deferred tax assets	(1,177)	(1,033)
Valuation allowance	17	20
Net deferred tax liabilities	574	578
Operating Loss Carryforwards [Line Items]
Deferred Tax Liabilities, Other Finite-Lived Assets	356	351
Deferred Tax Assets - Leasing Arrangement	392	374
Deferred Tax Assets, Leasehold Maintenance	(67)	$ (40)
Federal [Member]
Operating Loss Carryforwards [Line Items]
Income Taxes Receivable	285
Federal 1120 Refund [Member]
Operating Loss Carryforwards [Line Items]
Income Taxes Receivable	10
Other State Amended Return Refunds [Member]
Operating Loss Carryforwards [Line Items]
Income Taxes Receivable	12
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss	$ 325