Information by Operating Segment - Reconciliation of Consolidated Net Economic Earnings to Consolidated Net Income (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting [Abstract]
Net Income	$ 67.0	$ 67.3
Provision for ISRS rulings	2.6	0.0
Unrealized loss (gain) on energy-related derivatives	3.7	(2.2)
Acquisition, divestiture and restructuring activities	0.0	0.4
Income tax effect of adjustments	(1.5)	0.4
Net Economic Earnings	$ 71.8	$ 65.9