COMPONENTS OF PENSION AND OTHER POSTRETIREMENT BENEFIT (OPEB) PLANS NET PERIODIC BENEFIT COSTS - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions to pension trust			$ 1,995,000
Expected remaining contributions	$ 0		0
Settlement expense	0	$ 3,651,000	0	$ 17,347,000
Other Post-Employment Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected remaining contributions	0		0
Settlement expense	$ 0	$ 0	0	$ 0
Postemployment benefits paid			$ 25,454,000