Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Operating Activities:
Net Income	$ 290.6	$ 289.4
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	146.0	135.9
Deferred income taxes and investment tax credits	71.8	69.5
Changes in assets and liabilities:
Accounts receivable	(252.4)	(175.4)
Inventories	84.8	64.8
Regulatory assets and liabilities	147.5	317.6
Accounts payable	97.1	(34.6)
Delayed/advance customer billings, net	(57.7)	(47.7)
Taxes accrued	(23.7)	(21.5)
Other assets and liabilities	(55.1)	(41.7)
Other	4.9	3.1
Net cash provided by operating activities	453.8	559.4
Investing Activities:
Capital expenditures	(479.2)	(409.3)
Business acquisitions, net of cash acquired	0.0	(177.4)
Other	1.9	2.8
Net cash used in investing activities	(477.3)	(583.9)
Financing Activities:
Issuance of long-term debt	0.0	175.0
Repayment of long-term debt	(7.0)	(156.6)
Issuance (repayment) of short-term debt, net	68.0	(169.5)
Issuance of common stock	75.6	286.8
Dividends paid on common stock	(90.0)	(80.5)
Dividends paid on preferred stock	(7.4)	(7.4)
Other	(4.6)	(2.7)
Net cash provided by (used in) financing activities	34.6	45.1
Net Increase (Decrease) in Cash, Cash Equivalents, and Restricted Cash	11.1	20.6
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	25.8	34.9
Cash, Cash Equivalents, and Restricted Cash at End of Period	46.0	46.4
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(101.1)	(102.9)
Income taxes	(1.2)	(0.9)
Spire Missouri [Member]
Operating Activities:
Net Income	166.3	162.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	92.7	85.2
Deferred income taxes and investment tax credits	25.5	23.3
Changes in assets and liabilities:
Accounts receivable	(131.3)	(162.6)
Inventories	50.5	31.1
Regulatory assets and liabilities	146.7	276.5
Accounts payable	36.8	2.2
Delayed/advance customer billings, net	(56.0)	(46.7)
Taxes accrued	(12.3)	(13.2)
Other assets and liabilities	(40.2)	(10.2)
Other	0.5	0.8
Net cash provided by operating activities	279.2	348.6
Investing Activities:
Capital expenditures	(322.1)	(255.1)
Other	2.5	2.4
Net cash used in investing activities	(319.6)	(252.7)
Financing Activities:
Issuance (repayment) of short-term debt, net	0.0	200.0
Repayments of borrowings from Spire, net	(34.0)	(296.7)
Issuance of common stock	74.4	0.0
Net cash provided by (used in) financing activities	40.4	(96.7)
Net Increase (Decrease) in Cash, Cash Equivalents, and Restricted Cash	0.0	(0.8)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	0.0	0.8
Cash, Cash Equivalents, and Restricted Cash at End of Period	0.0	0.0
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(56.5)	(60.9)
Income taxes	(0.9)	(0.4)
Spire Alabama Inc [Member]
Operating Activities:
Net Income	85.7	81.8
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	35.7	36.1
Deferred income taxes and investment tax credits	28.7	27.7
Changes in assets and liabilities:
Accounts receivable	(49.1)	(30.4)
Inventories	9.0	18.2
Regulatory assets and liabilities	1.0	40.4
Accounts payable	21.1	2.9
Delayed/advance customer billings, net	(1.3)	(0.8)
Taxes accrued	(7.7)	(5.7)
Other assets and liabilities	(8.2)	3.1
Other	0.2	0.2
Net cash provided by operating activities	115.1	173.5
Investing Activities:
Capital expenditures	(63.1)	(43.6)
Other	0.4	0.3
Net cash used in investing activities	(62.7)	(43.3)
Financing Activities:
Repayments to Spire, net	(6.6)	(86.7)
Return of capital to Spire	(30.0)	(6.5)
Dividends paid on common stock	(14.0)	(36.4)
Net cash provided by (used in) financing activities	(50.6)	(129.6)
Net Increase (Decrease) in Cash, Cash Equivalents, and Restricted Cash	1.8	0.6
Cash, Cash Equivalents, and Restricted Cash at Beginning of Period	1.5	1.2
Cash, Cash Equivalents, and Restricted Cash at End of Period	3.3	1.8
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(14.9)	(17.7)
Income taxes	$ 0.0	$ 0.0