FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule of Realized Gain (Loss) [Table Text Block]

Activity for marketable securities (in millions):

	2017		2016		2015
Proceeds from sales and maturities	$	1,388	$	962	$	1,175

Schedule of Debt Investment Maturities [Table Text Block]

Maturities for marketable securities (in millions):

December 31, 2017	Cost Basis		Fair Value
Due in one year or less	$	113	$	113
Due after one year through five years	1,272		1,264
Due after five years through 10 years	50		50
Total	$	1,435	$	1,427

Fair Value, by Balance Sheet Grouping [Table Text Block]

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

December 31, 2017	Level 1		Level 2			Total
Assets
Marketable securities
U.S. government and agency securities	$	328	$	—		$	328
Foreign government bonds	—		43			43
Asset-backed securities	—		209			209
Mortgage-backed securities	—		99			99
Corporate notes and bonds	—		726			726
Municipal securities	—		22			22
Derivative instruments
Fuel hedge contracts—call options	—		22			22
Interest rate swap agreements	—		9			9
Liabilities
Derivative instruments
Interest rate swap agreements	—		(8		)	(8		)

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
Derivative instruments
Fuel hedge contracts—call options	—		20			20
Liabilities
Derivative instruments
Interest rate swap agreements	—		(5		)	(5		)

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

	2017		2016
Fixed rate debt at cost	$	956	$	1,175
Non-recurring purchase price accounting fair value adjustment	3		4
Total fixed rate debt	$	959	$	1,179
December 31, 2017 estimated fair value	$	959	$	1,199