INFORMATION BY OPERATING SEGMENT - Reconciliation of Consolidated Net Income to Consolidated Net Economic Earnings (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting [Abstract]
Net Income	$ (13.3)	$ 21.7	$ 108.0	$ 45.2	$ (14.2)	$ 10.7	$ 100.8	$ 46.9	$ 161.6	$ 144.2	$ 136.9
Unrealized loss (gain) on energy-related derivatives									6.0	(0.1)	(2.8)
Lower of cost or market inventory adjustments									0.0	0.2	0.4
Realized (gain) loss on economic hedges prior to the sale of the physical commodity									(0.3)	(1.6)	2.4
Acquisition, divestiture and restructuring activities									4.0	9.2	9.8
Gain on sale of property									0.0	0.0	(7.6)
Income tax effect of adjustments									(3.7)	(2.8)	(0.8)
Net Economic Earnings									$ 167.6	$ 149.1	$ 138.3