INCOME TAXES - DEFERRED TAX ASSETS AND LIABILITIES (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Excess of tax over book depreciation	$ 1,145	$ 1,126
Deferred Tax Liabilities, Intangible Assets	19	15
Deferred Tax Liabilities, Other	76	106
Gross deferred tax liabilities	1,591	1,589
Mileage Plan	(416)	(385)
Inventory obsolescence	(17)	(17)
Employee benefits	(127)	(215)
Net operating losses	(25)	(27)
Other - net	(34)	(103)
Deferred tax assets	(1,033)	(1,201)
Valuation allowance	20	19
Net deferred tax liabilities	578	407
Operating Loss Carryforwards [Line Items]
Deferred Tax Liabilities, Other Finite-Lived Assets	351	342
Deferred Tax Assets - Leasing Arrangement	374	381
Deferred Tax Assets, Leasehold Maintenance	(40)	$ (73)
Federal [Member]
Operating Loss Carryforwards [Line Items]
Income Taxes Receivable	285
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss	$ 413