Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating Activities:
Net Income	$ 289.4	$ 270.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	135.9	124.7
Deferred income taxes and investment tax credits	69.5	62.5
Changes in assets and liabilities:
Accounts receivable	(175.4)	43.7
Inventories	64.8	218.2
Regulatory assets and liabilities	317.6	(35.5)
Accounts payable	(34.6)	(372.9)
Delayed/advance customer billings, net	(47.7)	(76.3)
Taxes accrued	(21.5)	(10.8)
Other assets and liabilities	(41.7)	(50.6)
Other	3.1	6.7
Net cash provided by operating activities	559.4	179.9
Delayed/advance customer billings	(47.7)	(76.3)
Investing Activities:
Capital expenditures	(409.3)	(307.8)
Business acquisitions, net of cash acquired	(177.4)	(37.1)
Other	2.8	4.2
Net cash used in investing activities	(583.9)	(340.7)
Financing Activities:
Issuance of long-term debt	175.0	755.0
Repayment of long-term debt	(156.6)	(31.2)
Repayment of short-term debt, net	(169.5)	(476.5)
Issuance of common stock	286.8	3.6
Dividends paid on common stock	(80.5)	(74.5)
Dividends paid on preferred stock	(7.4)	(7.4)
Other financing activities	(2.7)	(7.5)
Net cash provided by financing activities	45.1	161.5
Net Increase in Cash, Cash Equivalents, and Restricted Cash	20.6	0.7
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	25.8	20.5
Cash, Cash Equivalents, and Restricted Cash at End of Period	46.4	21.2
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(102.9)	(80.5)
Income taxes	(0.9)	(1.4)
Spire Missouri [Member]
Operating Activities:
Net Income	162.2	159.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	85.2	77.8
Deferred income taxes and investment tax credits	23.3	24.8
Changes in assets and liabilities:
Accounts receivable	(162.6)	(208.9)
Inventories	31.1	126.2
Regulatory assets and liabilities	276.5	0.6
Accounts payable	2.2	(31.5)
Delayed/advance customer billings, net	(46.7)	(75.4)
Taxes accrued	(13.2)	(3.2)
Other assets and liabilities	(10.2)	(47.4)
Other	0.8	0.8
Net cash provided by operating activities	348.6	23.2
Delayed/advance customer billings	(46.7)	(75.4)
Investing Activities:
Capital expenditures	(255.1)	(206.6)
Other	2.4	1.8
Net cash used in investing activities	(252.7)	(204.8)
Financing Activities:
Issuance of long-term debt	0.0	400.0
Repayment of short-term debt, net	200.0	200.0
Dividends paid on common stock	0.0	(30.0)
Other financing activities	0.0	(3.9)
Net cash provided by financing activities	(96.7)	181.6
Net Increase in Cash, Cash Equivalents, and Restricted Cash	(0.8)	0.0
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	0.8	0.0
Cash, Cash Equivalents, and Restricted Cash at End of Period	0.0	0.0
Repayments of borrowings from Spire, net	(296.7)	(384.5)
Repayments of borrowings from Spire, net	(296.7)	(384.5)
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(60.9)	(44.1)
Income taxes	(0.4)	0.0
Spire Alabama Inc [Member]
Operating Activities:
Net Income	81.8	69.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	36.1	34.0
Deferred income taxes and investment tax credits	27.7	23.4
Changes in assets and liabilities:
Accounts receivable	(30.4)	(4.8)
Inventories	18.2	26.9
Regulatory assets and liabilities	40.4	(32.3)
Accounts payable	2.9	(39.2)
Delayed/advance customer billings, net	(0.8)	(0.7)
Taxes accrued	(5.7)	(4.9)
Other assets and liabilities	3.1	12.6
Other	0.2	0.2
Net cash provided by operating activities	173.5	84.4
Delayed/advance customer billings	(0.8)	(0.7)
Investing Activities:
Capital expenditures	(43.6)	(72.9)
Other	0.3	0.7
Net cash used in investing activities	(43.3)	(72.2)
Financing Activities:
Issuance of long-term debt	0.0	175.0
Dividends paid on common stock	(36.4)	(21.0)
Other financing activities	0.0	(1.0)
Net cash provided by financing activities	(129.6)	(13.6)
Net Increase in Cash, Cash Equivalents, and Restricted Cash	0.6	(1.4)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	1.2	2.4
Cash, Cash Equivalents, and Restricted Cash at End of Period	1.8	1.0
Repayments of borrowings from Spire, net	(86.7)	(139.6)
Repayments of borrowings from Spire, net	(86.7)	(139.6)
Return of capital to Spire	(6.5)	(27.0)
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(17.7)	(12.6)
Income taxes	$ 0.0	$ 0.0