Note 14 - Information by Operating Segment - Net Economic Earnings to Net Income (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Net Income	$ 217.5	$ 220.8	$ 271.7
Missouri regulatory adjustments	0.0	0.0	(9.0)
Fair value and timing adjustments	11.4	(11.4)	3.3
Acquisition and divestiture activities	2.5	0.0	(1.3)
Income tax adjustments	(3.3)	6.9	1.6
Net Economic Earnings	$ 228.1	$ 216.3	$ 266.3