FAIR VALUE MEASUREMENTS - Narrative (Details) gal in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) gal	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cost basis	$ 1,300
Sales and maturities of marketable securities	1,761	$ 1,152	$ 2,252
Net cash proceeds (payments) for fuel hedge positions		29	(130)
Accumulated other comprehensive income (loss)	(239)	(299)	(388)	$ (262)
Interest Income [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loss expected to be reclassified	$ 5
Commodity Contract, Settled Through March 2025 | Derivative Instruments Not Designated as Hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, volume | gal	20
Commodity Contract, Settled Through September 2025 | Derivative Instruments Not Designated as Hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, volume | gal	47
Fuel hedge contracts - call options | Derivative Instruments Not Designated as Hedges
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments		11
Gain (loss) on derivative instrument	$ (10)	(62)	93
Interest rate swap agreements | Derivative Instruments Designated as Hedges | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments	9	8
Gain (loss) on derivative instrument	7	8	(2)
Notional amount	567
Increase (decrease) in derivative assets	375
Accumulated other comprehensive income (loss)		$ (7)	$ 23
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt	$ 876