FAIR VALUE MEASUREMENTS (Tables)

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Investments Classified by Contractual Maturity Date

Maturities for marketable securities (in millions):

June 30, 2020	Cost Basis		Fair Value
Due in one year or less	$	133	$	134
Due after one year through five years	1,063		1,094
Due after five years through 10 years	60		61
Total	$	1,256	$	1,289

Fair Value, by Balance Sheet Grouping

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

	June 30, 2020						December 31, 2019
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets
Marketable securities
U.S. government and agency securities	$	281	$	—	$	281	$	330	$	—	$	330
Equity mutual funds	5		—		5		6		—		6
Foreign government bonds	—		22		22		—		31		31
Asset-backed securities	—		197		197		—		211		211
Mortgage-backed securities	—		214		214		—		176		176
Corporate notes and bonds	—		546		546		—		523		523
Municipal securities	—		29		29		—		23		23
Total Marketable securities	286		1,008		1,294		336		964		1,300
Derivative instruments
Fuel hedge—call options	—		5		5		—		11		11
Interest rate swap agreements	—		—		—		—		3		3
Total Assets	$	286	$	1,013	$	1,299	$	336	$	978	$	1,314
Liabilities
Derivative instruments
Interest rate swap agreements	—		(33)		(33)		—		(10)		(10)
Total Liabilities	$	—	$	(33)	$	(33)	$	—	$	(10)	$	(10)

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

	June 30, 2020		December 31, 2019
Fixed-rate debt at cost	$	444	$	473
Non-recurring purchase price accounting fair value adjustment	2		2
Total fixed-rate debt	$	446	$	475
Estimated fair value	$	463	$	483