EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		1 Months Ended	3 Months Ended								12 Months Ended
	Jun. 11, 2014	Jun. 30, 2014	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Basic EPS:
Net income			$ (14.2)	$ 10.7	$ 100.8	$ 46.9	$ (18.7)	$ 14.1	$ 94.4	$ 47.1	$ 144.2	$ 136.9	$ 84.6
Less: Income allocated to participating securities											0.5	0.5	0.3
Net Income Available to Common Shareholders											$ 143.7	$ 136.4	$ 84.3
Weighted Average Shares Outstanding, Basic (in Shares)											44.1	43.2	35.8
Earnings Per Share of Common Stock (in dollars per share)			$ (0.31)	$ 0.24	$ 2.32	$ 1.08	$ (0.43)	$ 0.32	$ 2.18	$ 1.09	$ 3.26	$ 3.16	$ 2.36
Diluted EPS:
Net income			$ (14.2)	$ 10.7	$ 100.8	$ 46.9	$ (18.7)	$ 14.1	$ 94.4	$ 47.1	$ 144.2	$ 136.9	$ 84.6
Less: Income allocated to participating securities											0.5	0.5	0.3
Net Income Available to Common Shareholders											$ 143.7	$ 136.4	$ 84.3
Weighted Average Shares Outstanding, Basic (in Shares)											44.1	43.2	35.8
Dilutive Effect of Stock Options, Restricted Stock, and Restricted Stock Units (in shares)											0.2	0.1	0.1
Weighted Average Diluted Shares (in shares)											44.3	43.3	35.9
Earnings Per Share of Common Stock (in dollars per share)			$ (0.31)	$ 0.24	$ 2.31	$ 1.08	$ (0.43)	$ 0.32	$ 2.18	$ 1.09	$ 3.24	$ 3.16	$ 2.35
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Equity units, contract annual rate	4.75%	2.00%
Restricted stock and stock units subject to performance and/or market conditions
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding shares excluded from calculation of diluted EPS (in shares)											0.3	0.3	0.3