FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Investments Classified by Contractual Maturity Date

Maturities for marketable securities (in millions):

March 31, 2020	Cost Basis		Fair Value
Due in one year or less	$	167	$	166
Due after one year through five years	1,092		1,102
Due after five years through 10 years	41		41
Total	$	1,300	$	1,309

Fair Value, by Balance Sheet Grouping

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

	March 31, 2020						December 31, 2019
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets
Marketable securities
U.S. government and agency securities	$	305	$	—	$	305	$	330	$	—	$	330
Equity mutual funds	4		—		4		6		—		6
Foreign government bonds	—		26		26		—		31		31
Asset-backed securities	—		206		206		—		211		211
Mortgage-backed securities	—		213		213		—		176		176
Corporate notes and bonds	—		537		537		—		523		523
Municipal securities	—		23		23		—		23		23
Total Marketable securities	309		1,005		1,314		336		964		1,300
Derivative instruments
Fuel hedge—call options	—		1		1		—		11		11
Interest rate swap agreements	—		—		—		—		3		3
Total Assets	$	309	$	1,006	$	1,315	$	336	$	978	$	1,314
Liabilities
Derivative instruments
Interest rate swap agreements	—		(31)		(31)		—		(10)		(10)
Total Liabilities	$	—	$	(31)	$	(31)	$	—	$	(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):

	March 31, 2020		December 31, 2019
Fixed-rate debt at cost	$	455	$	473
Non-recurring purchase price accounting fair value adjustment	2		2
Total fixed-rate debt	$	457	$	475
Estimated fair value	$	487	$	483