FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value, by Balance Sheet Grouping [Table Text Block]

Fair values of financial instruments on the consolidated balance sheet (in millions):

	December 31, 2023						December 31, 2022
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets
Marketable securities
U.S. government and agency securities	$	387	$	—	$	387	$	505	$	—	$	505
Equity mutual funds	5		—		5		5		—		5
Foreign government bonds	—		10		10		—		25		25
Asset-backed securities	—		192		192		—		261		261
Mortgage-backed securities	—		115		115		—		196		196
Corporate notes and bonds	—		763		763		—		1,025		1,025
Municipal securities	—		38		38		—		62		62
Total Marketable securities	392		1,118		1,510		510		1,569		2,079
Derivative instruments
Fuel hedge contracts - call options	—		11		11		—		44		44
Interest rate swap agreements	—		8		8		—		15		15
Total Assets	$	392	$	1,137	$	1,529	$	510	$	1,628	$	2,138

Fixed-rate debt on the consolidated balance sheet and the estimated fair value of long-term fixed-rate debt (in millions):

	December 31, 2023		December 31, 2022
Fixed-rate debt	$	1,515	$	1,660
Estimated fair value	$	1,382	$	1,473

Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis

Certain assets and liabilities are recognized or disclosed at fair value on a nonrecurring basis, including property, plant and equipment, operating lease assets, goodwill, and intangible assets. These assets are subject to fair valuation when there is evidence of impairment. Refer to Note 2 for discussion regarding impairment charges recorded in the year.

Schedule of Realized Gain (Loss) [Table Text Block]

Proceeds from sales of marketable securities were $1.2 billion, $2.3 billion, and $3.6 billion in 2023, 2022, and 2021.

Schedule of Debt Investment Maturities [Table Text Block]

Maturities for marketable securities (in millions):

December 31, 2023	Cost Basis		Fair Value
Due in one year or less	$	372	$	366
Due after one year through five years	1,126		1,091
Due after five years through nine years	36		33
Due after 10 years	17		15
No maturity date	4		5
Total	$	1,555	$	1,510