FAIR VALUE MEASUREMENTS (Tables)

9 Months Ended

Sep. 30, 2021

Fair Value Disclosures [Abstract]

Investments Classified by Contractual Maturity Date

Maturities for marketable securities (in millions):

September 30, 2021	Cost Basis		Fair Value
Due in one year or less	$	1,193	$	1,194
Due after one year through five years	1,409		1,418
Due after five years through 10 years	81		81
Total	$	2,683	$	2,693

Fair Value, by Balance Sheet Grouping

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

	September 30, 2021						December 31, 2020
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets
Marketable securities
U.S. government and agency securities	$	278	$	—	$	278	$	407	$	—	$	407
Equity mutual funds	6		—		6		7		—		7
Foreign government bonds	—		38		38		—		20		20
Asset-backed securities	—		337		337		—		224		224
Mortgage-backed securities	—		239		239		—		290		290
Corporate notes and bonds	—		1,736		1,736		—		978		978
Municipal securities	—		66		66		—		50		50
Total Marketable securities	284		2,416		2,700		414		1,562		1,976
Derivative instruments
Fuel hedge - call options	—		95		95		—		15		15
Total Assets	$	284	$	2,511	$	2,795	$	414	$	1,577	$	1,991
Liabilities
Derivative instruments
Interest rate swap agreements	—		(14)		(14)		—		(25)		(25)
Total Liabilities	$	—	$	(14)	$	(14)	$	—	$	(25)	$	(25)

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

	September 30, 2021		December 31, 2020
Total fixed-rate debt	$	1,828	$	1,662
Estimated fair value	$	1,949	$	1,778