Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Operating Activities:
Net Income (Loss)	$ 271.7	$ 250.9	$ 217.5
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	298.2	278.4	254.8
Deferred income taxes and investment tax credits	57.3	57.0	36.9
Changes in assets and liabilities:
Accounts receivable	(38.4)	12.7	334.2
Inventories	(18.6)	15.8	142.8
Regulatory assets and liabilities	26.5	341.4	(68.7)
Accounts payable	47.5	(25.1)	(389.2)
Delayed/advance customer billings, net	8.1	37.5	1.5
Taxes accrued	6.0	1.1	15.0
Other assets and liabilities	(93.4)	(65.6)	(117.6)
Other	13.1	8.3	13.0
Net cash provided by operating activities	578.0	912.4	440.2
Investing Activities:
Capital expenditures	(922.4)	(861.3)	(662.5)
Business acquisition, net of cash acquired	0.0	(175.9)	(37.0)
Other	6.0	10.0	4.0
Net cash used in investing activities	(916.4)	(1,027.2)	(695.5)
Financing Activities:
Issuance of long-term debt	150.0	495.0	755.0
Repayment of long-term debt	(42.0)	(456.6)	(281.2)
Issuance (repayment) of short-term debt, net	370.0	(8.5)	(82.0)
Issuance of common stock	76.2	287.0	41.9
Dividends paid on common stock	(182.2)	(167.1)	(150.7)
Dividends paid on preferred stock	(14.8)	(14.8)	(14.8)
Other	(12.5)	(11.1)	(7.6)
Net cash provided by (used in) financing activities	344.7	123.9	260.6
Net Increase (Decrease) in Cash and Cash Equivalents	6.3	9.1	5.3
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	34.9	25.8	20.5
Cash, Cash Equivalents, and Restricted Cash at End of Year	41.2	34.9	25.8
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(207.1)	(205.6)	(177.5)
Income taxes	(2.9)	(0.9)	(2.0)
Spire Missouri [Member]
Operating Activities:
Net Income (Loss)	128.3	118.4	117.5
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	188.4	174.0	158.7
Deferred income taxes and investment tax credits	13.6	14.8	11.6
Changes in assets and liabilities:
Accounts receivable	(9.3)	(14.2)	16.0
Inventories	(20.5)	3.0	80.2
Regulatory assets and liabilities	22.0	310.8	(22.4)
Accounts payable	28.6	(5.3)	(45.7)
Delayed/advance customer billings, net	9.2	36.7	2.2
Taxes accrued	5.9	0.1	9.7
Other assets and liabilities	(25.2)	(65.2)	(108.4)
Other	2.7	1.4	1.7
Net cash provided by operating activities	343.7	574.5	221.1
Investing Activities:
Capital expenditures	(641.2)	(553.0)	(447.5)
Other	4.5	6.7	4.1
Net cash used in investing activities	(636.7)	(546.3)	(443.4)
Financing Activities:
Issuance of long-term debt	150.0	320.0	400.0
Repayment of long-term debt	0.0	(300.0)	(250.0)
Borrowings (repayments to) from Spire, net	71.0	(45.3)	95.3
Issuance of common stock	74.4	0.0	38.7
Dividends paid on common stock	0.0	0.0	(57.0)
Other	(2.4)	(3.7)	(3.9)
Net cash provided by (used in) financing activities	293.0	(29.0)	223.1
Net Increase (Decrease) in Cash and Cash Equivalents	0.0	(0.8)	0.8
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	0.0	0.8	0.0
Cash, Cash Equivalents, and Restricted Cash at End of Year	0.0	0.0	0.8
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(102.9)	(111.6)	(93.8)
Income taxes	(0.9)	(0.4)	(0.2)
Spire Alabama Inc [Member]
Operating Activities:
Net Income (Loss)	84.9	80.1	66.0
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	71.0	72.8	69.3
Deferred income taxes and investment tax credits	28.4	26.9	20.3
Changes in assets and liabilities:
Accounts receivable	(0.5)	8.0	27.1
Inventories	(2.4)	15.6	17.2
Regulatory assets and liabilities	2.7	49.3	(49.5)
Accounts payable	8.8	2.4	(42.3)
Delayed/advance customer billings, net	(1.1)	0.7	(0.6)
Taxes accrued	(1.7)	0.3	3.3
Other assets and liabilities	(38.5)	(8.6)	18.7
Other	0.9	0.4	0.4
Net cash provided by operating activities	152.5	247.9	129.9
Investing Activities:
Capital expenditures	(144.2)	(112.8)	(117.6)
Other	0.9	0.8	1.3
Net cash used in investing activities	(143.3)	(112.0)	(116.3)
Financing Activities:
Issuance of long-term debt	0.0	0.0	175.0
Repayment of long-term debt	(35.0)	0.0	0.0
Borrowings (repayments to) from Spire, net	81.7	(75.7)	(136.8)
Return of capital to Spire	(36.5)	(6.5)	(31.0)
Dividends paid on common stock	(18.6)	(53.4)	(21.0)
Other	(0.4)	0.0	(1.0)
Net cash provided by (used in) financing activities	(8.8)	(135.6)	(14.8)
Net Increase (Decrease) in Cash and Cash Equivalents	0.4	0.3	(1.2)
Cash, Cash Equivalents, and Restricted Cash at Beginning of Year	1.5	1.2	2.4
Cash, Cash Equivalents, and Restricted Cash at End of Year	1.9	1.5	1.2
Supplemental disclosure of cash paid for:
Interest, net of amounts capitalized	(28.9)	(32.9)	(30.1)
Income taxes	$ 0.0	$ 0.0	$ 0.0