INCOME TAXES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
DEFERRED TAX LIABILITIES:
Accelerated depreciation	$ 3,595	$ 3,279
Prepaid insurance	258	238
Operating lease liabilities	276	311
Other	91	154
Total deferred tax liabilities	4,220	3,982
DEFERRED TAX ASSETS:
Accrued employee benefits	757	424
Loyalty program and flight credit liability	599	659
Operating lease liabilities	279	313
Net operating losses and tax credits (a)	309	310
Other	232	291
Total deferred tax assets	2,176	1,997
Net deferred tax liability	2,044	1,985
CURRENT:
Federal	(10)	(36)	$ 337
State	19	(3)	33
Change in federal statutory rate	0	0	(2)
Total current	9	(39)	368
DEFERRED:
Federal	140	208	(43)
State	19	20	23
Total deferred	159	228	(20)
Total income tax provision (benefit)	168	189	348
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax at statutory U.S. tax rates	133	153	278
State income taxes, net of federal benefit	30	12	45
Change in federal statutory tax rate	0	0	(2)
Convertible debt repurchases	0	31	21
DOT settlement	22	0	0
Federal tax credits	(19)	(13)	(2)
Other, net	2	6	8
Total income tax provision (benefit)	168	189	$ 348
State and Local Jurisdiction
DEFERRED TAX ASSETS:
Operating loss carryforwards	36	43
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating loss carryforwards	36	43
Domestic Tax Authority
DEFERRED TAX ASSETS:
Operating loss carryforwards	268	275
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating loss carryforwards	$ 268	$ 275