EARNINGS PER COMMON SHARE (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Apr. 03, 2017	Sep. 30, 2016
Basic EPS:
Net Income		$ 108.0	$ 100.8	$ 153.2	$ 147.7
Less: Income allocated to participating securities		0.2	0.3	0.4	0.5
Net Income Available to Common Shareholders		$ 107.8	$ 100.5	$ 152.8	$ 147.2
Weighted Average Shares Outstanding, Basic (in Shares)		45,600,000	43,300,000	45,600,000	43,300,000
Basic Earnings Per Share of Common Stock (in dollars per share)		$ 2.36	$ 2.32	$ 3.35	$ 3.40
Diluted EPS:
Net Income		$ 108.0	$ 100.8	$ 153.2	$ 147.7
Less: Income allocated to participating securities		0.2	0.3	0.4	0.5
Net Income Available to Common Shareholders		$ 107.8	$ 100.5	$ 152.8	$ 147.2
Weighted Average Shares Outstanding, Basic (in Shares)		45,600,000	43,300,000	45,600,000	43,300,000
Dilutive Effect of Stock Options, Restricted Stock and Restricted Stock Units (in shares)		100,000	200,000	100,000	200,000
Weighted Average Diluted Shares (in shares)		45,700,000	43,500,000	45,700,000	43,500,000
Diluted Earnings Per Share of Common Stock (in dollars per share)		$ 2.36	$ 2.31	$ 3.34	$ 3.39
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock, issued (in shares)		45,700,000	43,400,000	45,700,000	43,400,000		45,600,000
Equity units, contract annual rate	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)		500,000	400,000	500,000	400,000
Subsequent Event
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock, issued (in shares)						2,500,000.0