Note 13 - Pension Plans and Other Postretirement Benefits - Expected Pension Benefit Payments for Succeeding Fiscal Years (Details) $ in Millions	Sep. 30, 2024 USD ($)
Pension Plan [Member]
2025	$ 49.4
2026	45.6
2027	44.5
2028	44.0
2029	43.0
2030-2035	197.8
Pension Plan [Member] \| Spire Missouri [Member]
2025	38.2
2026	34.0
2027	32.0
2028	31.4
2029	30.2
2030-2035	132.7
Pension Plan [Member] \| Spire Alabama Inc [Member]
2025	7.6
2026	7.9
2027	8.8
2028	8.5
2029	8.9
2030-2035	45.4
Other Postretirement Benefits Plan [Member]
2025	14.5
2026	14.1
2027	13.6
2028	13.0
2029	12.6
2030-2035	58.1
Other Postretirement Benefits Plan [Member] \| Spire Missouri [Member]
2025	11.3
2026	10.8
2027	10.4
2028	9.9
2029	9.5
2030-2035	42.7
Other Postretirement Benefits Plan [Member] \| Spire Alabama Inc [Member]
2025	3.1
2026	3.1
2027	3.1
2028	3.0
2029	3.0
2030-2035	$ 14.9

Amount of benefit for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following current fiscal year.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480506/715-20-50-1

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