FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Schedule of assets (liabilities) measured at fair value on a recurring basis

Assets (Liabilities) Measured at Fair Value on a Recurring Basis(1)

	December 31, 2023								Valuation Technique
(in millions)	Total		Level 1		Level 2		Level 3
Cash equivalents	$	1,545	$	1,545	$	—	$	—	(a)
Restricted cash equivalents	653		653		—		—		(a)
Short-term investments
U.S. Government securities	859		204		655		—		(a)
Corporate obligations	218		—		218		—		(a)
Other fixed income securities	50		—		50		—		(a)
Long-term investments and related	2,867		2,614		134		119		(a)(b)
Hedge derivatives, net
Fuel hedge contracts	5		—		5		—		(a)(b)

	December 31, 2022								Valuation Technique
(in millions)	Total		Level 1		Level 2		Level 3
Cash equivalents	$	2,021	$	2,021	$	—	$	—	(a)
Restricted cash equivalents	206		206		—		—		(a)
Short-term investments
U.S. Government securities	1,587		122		1,465		—		(a)
Corporate obligations	1,614		—		1,614		—		(a)
Other fixed income securities	67		—		67		—		(a)
Long-term investments	1,450		1,305		38		107		(a)(b)
Hedge derivatives, net
Fuel hedge contracts	(47)		—		(47)		—		(a)(b)

(1)See Note 9, "Employee Benefit Plans," for fair value of benefit plan assets.