Note 9 - Information by Operating Segment - Net Economic Earnings to Net Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Net Income	$ (1.4)	$ 5.3	$ 227.9	$ 281.6
Missouri regulatory adjustment	0.0	0.0	0.0	(9.0)
Fair value and timing adjustments	7.3	2.1	20.9	6.2
Income tax adjustments	(1.8)	(0.5)	(1.1)	0.6
Net Economic Earnings	$ 4.1	$ 6.9	$ 247.7	$ 279.4