FAIR VALUE MEASUREMENTS (Tables)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Fair Value, Assets Measured on Recurring Basis

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

September 30, 2017	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	359	$	—		$	359
Foreign government bonds	—		48			48
Asset-backed securities	—		232			232
Mortgage-backed securities	—		113			113
Corporate notes and bonds	—		828			828
Municipal securities	—		16			16
Total Marketable securities	359		1,237			1,596
Derivative instruments
Fuel hedge call options	—		10			10
Interest rate swap agreements	—		8			8
Total Assets	359		1,255			1,614
Liabilities
Derivative instruments
Interest rate swap agreements	—		(11		)	(11		)
Total Liabilities	—		(11		)	(11		)

December 31, 2016	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	287	$	—		$	287
Foreign government bonds	—		36			36
Asset-backed securities	—		138			138
Mortgage-backed securities	—		89			89
Corporate notes and bonds	—		691			691
Municipal securities	—		11			11
Total Marketable securities	287		965			1,252
Derivative instruments
Fuel hedge call options	—		20			20
Total Assets	287		985			1,272
Liabilities
Derivative instruments
Interest rate swap agreements	—		(5		)	(5		)
Total Liabilities	—		(5		)	(5		)

Fair Value, Liabilities Measured on Recurring Basis

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

September 30, 2017	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	359	$	—		$	359
Foreign government bonds	—		48			48
Asset-backed securities	—		232			232
Mortgage-backed securities	—		113			113
Corporate notes and bonds	—		828			828
Municipal securities	—		16			16
Total Marketable securities	359		1,237			1,596
Derivative instruments
Fuel hedge call options	—		10			10
Interest rate swap agreements	—		8			8
Total Assets	359		1,255			1,614
Liabilities
Derivative instruments
Interest rate swap agreements	—		(11		)	(11		)
Total Liabilities	—		(11		)	(11		)

December 31, 2016	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	287	$	—		$	287
Foreign government bonds	—		36			36
Asset-backed securities	—		138			138
Mortgage-backed securities	—		89			89
Corporate notes and bonds	—		691			691
Municipal securities	—		11			11
Total Marketable securities	287		965			1,252
Derivative instruments
Fuel hedge call options	—		20			20
Total Assets	287		985			1,272
Liabilities
Derivative instruments
Interest rate swap agreements	—		(5		)	(5		)
Total Liabilities	—		(5		)	(5		)

Activity for Marketable Securities

Activity for marketable securities (in millions):  

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Proceeds from sales and maturities	$	528	$	280	$	1,069	$	638

Investments Classified by Contractual Maturity Date

Maturities for marketable securities (in millions):

September 30, 2017	Cost Basis		Fair Value
Due in one year or less	$	193	$	193
Due after one year through five years	1,367		1,367
Due after five years through 10 years	36		36
Due after 10 years	—		—
Total	$	1,596	$	1,596

Fair Value, by Balance Sheet Grouping

Fixed-rate debt that is not carried at fair value on the consolidated balance sheet and the estimated fair value of long-term fixed-rate debt is as follows (in millions):

	September 30, 2017		December 31, 2016
Carrying amount	$	1,024	$	1,179
Fair value	1,034		1,199