FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 3,368		$ 3,368		$ 3,268
Short-term investments expected to mature in one year or less	3,100		3,100
Fuel hedge contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) on derivatives recognized	$ 12	$ (239)	43	$ (478)
Fuel hedge contracts | Mark-to-Market
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain on derivative			39
Fuel hedge contracts | Settlement Gains On Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain on derivative			$ 4