PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Additional Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Effect of change in mine ownership & noncontrolling interest	$ 14.2	$ 48.4	$ 51.2
Actual return on plan assets	54.8	(6.4)	59.1
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Effect of change in mine ownership & noncontrolling interest	5.9	5.5	5.9
Actual return on plan assets	$ 16.0	$ (3.9)	$ 31.9