FAIR VALUE MEASUREMENTS (Tables)

6 Months Ended

Jun. 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):

June 30, 2017	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	448	$	—		$	448
Foreign government bonds	—		39			39
Asset-backed securities	—		222			222
Mortgage-backed securities	—		113			113
Corporate notes and bonds	—		889			889
Municipal securities	—		13			13
Total Marketable securities	448		1,276			1,724
Derivative instruments
Fuel hedge call options	—		8			8
Interest rate swap agreements	—		8			8
Total Assets	448		1,292			1,740
Liabilities
Derivative instruments
Interest rate swap agreements	—		(12		)	(12		)
Total Liabilities	—		(12		)	(12		)

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):

June 30, 2017	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	448	$	—		$	448
Foreign government bonds	—		39			39
Asset-backed securities	—		222			222
Mortgage-backed securities	—		113			113
Corporate notes and bonds	—		889			889
Municipal securities	—		13			13
Total Marketable securities	448		1,276			1,724
Derivative instruments
Fuel hedge call options	—		8			8
Interest rate swap agreements	—		8			8
Total Assets	448		1,292			1,740
Liabilities
Derivative instruments
Interest rate swap agreements	—		(12		)	(12		)
Total Liabilities	—		(12		)	(12		)

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 June 30,						Six Months Ended June 30,
	2017			2016			2017			2016
Proceeds from sales and maturities	$	256		$	217		$	541		$	357
Gross realized gains	—			2			1			2
Gross realized losses	(1		)	(1		)	(2		)	(1		)

Unrealized gains and losses (in millions):

	June 30, 2017		December 31, 2016
Unrealized gains	4		2
Unrealized losses	(5	)	(7	)

Investments Classified by Contractual Maturity Date

Maturities for marketable securities (in millions):

June 30, 2017	Cost Basis		Fair Value
Due in one year or less	$	253	$	252
Due after one year through five years	1,453		1,453
Due after five years through 10 years	19		19
Due after 10 years	—		—
Total	$	1,725	$	1,724

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):

	June 30, 2017		December 31, 2016
Carrying amount	$	1,090	$	1,179
Fair value	1,105		1,199