PENSION AND OTHER POSTRETIREMENT BENEFIT PLANS - Actual Returns on Assets Held by Our Pension Trusts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets	$ 1.00	$ 1.00	$ 1.00
Direct investments
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets	0.72	0.44	0.77
Derivative instruments
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets	$ 0.28	$ 0.56	$ 0.23