Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Net Income	$ 217.5	$ 220.8	$ 271.7
Other Comprehensive Income, Before Tax:
Net hedging gain arising during the period	20.1	56.7	61.2
Amounts reclassified into regulatory liabilities	(17.5)	0.0	0.0
Amounts reclassified into net income	(2.4)	(1.2)	(1.3)
Net gain on cash flow hedging derivative instruments	0.2	55.5	59.9
Net gain (loss) on defined benefit pension and other postretirement plans	0.2	1.5	(1.3)
Net unrealized gain (loss) on available-for-sale debt securities	0.1	(0.4)	(0.2)
Other Comprehensive Income, Before Tax	0.5	56.6	58.4
Income Tax Expense Related to Items of Other Comprehensive Income	0.1	13.0	13.6
Other Comprehensive Income, Net of Tax	0.4	43.6	44.8
Comprehensive Income	$ 217.9	$ 264.4	$ 316.5