INCOME TAXES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
DEFERRED TAX LIABILITIES:
Accelerated depreciation	$ 3,351	$ 3,595
Prepaid insurance	282	258
Operating lease right-of-use assets	314	276
Other	99	91
Total deferred tax liabilities	4,046	4,220
DEFERRED TAX ASSETS:
Accrued employee benefits	337	757
Loyalty program and flight credit liability	604	599
Operating lease liabilities	319	279
Net operating losses and tax credits	352	309
Other	267	232
Total deferred tax assets	1,879	2,176
Net deferred tax liability	2,167	2,044
CURRENT:
Federal	0	(10)	$ (36)
State	1	19	(3)
Total current	1	9	(39)
DEFERRED:
Federal	108	140	208
State	24	19	20
Total deferred	132	159	228
Total income tax provision (benefit)	133	168	189
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax at statutory U.S. tax rates	126	133	153
State income taxes, net of federal benefit	20	30	12
Nondeductible per diem	9	8	1
Convertible debt repurchases	0	0	31
DOT settlement	(3)	22	0
Federal tax credits	(33)	(19)	(13)
Other, net	14	(6)	5
Total income tax provision (benefit)	133	168	$ 189
State and Local Jurisdiction
DEFERRED TAX ASSETS:
Operating loss carryforwards	56	36
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating loss carryforwards	56	36
Domestic Tax Authority
DEFERRED TAX ASSETS:
Operating loss carryforwards	253	268
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating loss carryforwards	$ 253	$ 268