PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Funded Status of Our Plans (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	$ (40)	$ (49)
Pension
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,514	5,351	$ 5,491
Projected benefit obligations	(6,795)	(6,469)	(6,211)
Noncurrent assets	45	27
Current liabilities	(21)	(28)
Noncurrent liabilities	(1,305)	(1,117)
Funded status	(1,281)	(1,118)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0	0
Projected benefit obligations	(200)	(225)	$ (240)
Noncurrent assets	0	0
Current liabilities	(19)	(21)
Noncurrent liabilities	(181)	(204)
Funded status	$ (200)	$ (225)