FAIR VALUE MEASUREMENTS (Tables)

6 Months Ended

Jun. 30, 2024

Fair Value Disclosures [Abstract]

Investments Classified by Contractual Maturity Date

Maturities for marketable securities (in millions):

June 30, 2024	Cost Basis		Fair Value
Due in one year or less	$	600	$	592
Due after one year through five years	785		758
Due after five years through ten years	29		26
Due after 10 years	13		12
No maturity date	4		6
Total	$	1,431	$	1,394

Fair Value, by Balance Sheet Grouping

Fair values of financial instruments on the unaudited Condensed Consolidated Balance Sheets (in millions):

	June 30, 2024						December 31, 2023
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets
Marketable securities
U.S. government and agency securities	$	438	$	—	$	438	$	387	$	—	$	387
Equity mutual funds	6		—		6		5		—		5
Foreign government bonds	—		10		10		—		10		10
Asset-backed securities	—		168		168		—		192		192
Mortgage-backed securities	—		91		91		—		115		115
Corporate notes and bonds	—		638		638		—		763		763
Municipal securities	—		43		43		—		38		38
Total Marketable securities	444		950		1,394		392		1,118		1,510
Derivative instruments
Fuel hedge contracts - call options	—		6		6		—		11		11
Interest rate swap agreements	—		9		9		—		8		8
Total Assets	$	444	$	965	$	1,409	$	392	$	1,137	$	1,529

Fixed-rate debt on the unaudited Condensed Consolidated Balance Sheets and the estimated fair value of long-term fixed-rate debt (in millions):

	June 30, 2024		December 31, 2023
Fixed-rate debt	$	1,447	$	1,515
Estimated fair value	$	1,367	$	1,382