Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Net Income (Loss)	$ 271.7	$ 250.9	$ 217.5
Other Comprehensive Income (Loss), Before Tax:
Net hedging gain (loss) arising during the period	12.8	(15.9)	20.1
Amounts reclassified into regulatory liabilities	0.0	(20.1)	(17.5)
Amounts reclassified into net income	(5.1)	(11.1)	(2.4)
Net gain (loss) on cash flow hedging derivative instruments	7.7	(47.1)	0.2
Net gain on defined benefit pension and other postretirement plans	1.3	0.6	0.2
Net unrealized gain on available-for-sale debt securities	0.1	0.2	0.1
Other Comprehensive Income (Loss), Before Tax	9.1	(46.3)	0.5
Income Tax Expense (Benefit) Related to Items of Other Comprehensive Income	1.8	(10.8)	0.1
Other Comprehensive Income (Loss), Net of Tax	7.3	(35.5)	0.4
Comprehensive Income	279.0	215.4	217.9
Operating Revenues	2,476.4	2,593.0	2,666.3
Operating Expenses:
Natural gas	905.5	1,103.3	1,260.8
Operation and maintenance	542.1	507.4	517.6
Depreciation and amortization expense	298.2	278.4	254.8
Taxes, other than income taxes	206.7	215.6	214.5
Total Operating Expenses	1,952.5	2,104.7	2,247.7
Operating Income	523.9	488.3	418.6
Interest Expense	204.1	201.1	185.7
Other Income, Net	11.6	22.4	23.4
Income Before Income Taxes	331.4	309.6	256.3
Income Tax Expense	59.7	58.7	38.8
Net Income	271.7	250.9	217.5
Spire Missouri [Member]
Net Income (Loss)	128.3	118.4	117.5
Other Comprehensive Income (Loss), Before Tax:
Other Comprehensive Income (Loss), Net of Tax	1.3	0.5	0.2
Comprehensive Income	129.6	118.9	117.7
Operating Revenues	1,544.1	1,737.4	1,762.9
Operating Expenses:
Natural gas	669.4	886.2	943.4
Operation and maintenance	300.7	287.4	296.2
Depreciation and amortization expense	188.4	174.0	158.7
Taxes, other than income taxes	151.1	157.7	157.5
Total Operating Expenses	1,309.6	1,505.3	1,555.8
Operating Income	234.5	232.1	207.1
Interest Expense	100.2	106.4	97.4
Other Income, Net	7.8	8.4	19.4
Income Before Income Taxes	142.1	134.1	129.1
Income Tax Expense	13.8	15.7	11.6
Net Income	$ 128.3	$ 118.4	$ 117.5