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, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting [Abstract]
Net income	$ (18.7)	$ 14.1	$ 94.4	$ 47.1	$ (14.9)	$ 11.7	$ 52.2	$ 35.6	$ 136.9	$ 84.6	$ 52.8
Unrealized loss (gain) on energy-related derivatives									(1.8)	(0.9)	0.5
Lower of cost or market inventory adjustments									0.3	(0.7)	0.9
Realized (gain) loss on economic hedges prior to the sale of the physical commodity									1.5	(0.2)	0.0
Acquisition, divestiture and restructuring activities									6.1	17.3	10.8
Gain on sale of property									(4.7)	0.0	0.0
Net Economic Earnings (Non-GAAP)									$ 138.3	$ 100.1	$ 65.0