FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Investments Classified by Contractual Maturity Date

Maturities for marketable securities (in millions):

March 31, 2024	Cost Basis		Fair Value
Due in one year or less	$	443	$	436
Due after one year through five years	939		907
Due after five years	34		31
Due after 10 years	14		13
No maturity date	4		6
Total	$	1,434	$	1,393

Fair Value, by Balance Sheet Grouping

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

	March 31, 2024						December 31, 2023
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets
Marketable securities
U.S. government and agency securities	$	370	$	—	$	370	$	387	$	—	$	387
Equity mutual funds	6		—		6		5		—		5
Foreign government bonds	—		10		10		—		10		10
Asset-backed securities	—		170		170		—		192		192
Mortgage-backed securities	—		103		103		—		115		115
Corporate notes and bonds	—		695		695		—		763		763
Municipal securities	—		39		39		—		38		38
Total Marketable securities	376		1,017		1,393		392		1,118		1,510
Derivative instruments
Fuel hedge contracts - call options	—		11		11		—		11		11
Interest rate swap agreements	—		9		9		—		8		8
Total Assets	$	376	$	1,037	$	1,413	$	392	$	1,137	$	1,529

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

	March 31, 2024		December 31, 2023
Fixed-rate debt	$	1,452	$	1,515
Estimated fair value	$	1,346	$	1,382