ACCOUNTING POLICIES (Detail Textuals) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Acquisition-related costs	$ 12.8	$ 48.8	$ 123.4
Gain on disposition of former manufacturing facility	3.3
Gain in Other Operating Income due to insurance recoveries at Becancour			42.3
Gain in Other Operating Income due to insurance recoveries at McIntosh			3.7
Short-term investments	0.0	0.0
Asset retirement obligation non-current portion	43.8	42.8
Asset retirement obligation revision of estimate	4.5	7.4
Goodwill Impairment Loss	0.0	0.0	0.0
Impairment of Intangible Assets, Finite-lived	$ 0.0	$ 0.0	$ 0.0
Average remaining life expectancy of the inactive participants in the defined benefit pension plan (in years)	19 years	19 years