Information by Operating Segment - Reconciliation of Consolidated Net Economic Earnings to Consolidated Net Income (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting [Abstract]
Net Income	$ 88.9	$ 67.0
Provision for ISRS rulings	0.0	2.6
Fair value and timing adjustments	(16.0)	3.7
Income tax effect of adjustments	4.0	(1.5)
Net Economic Earnings	$ 76.9	$ 71.8