Note 13 - Pension Plans and Other Postretirement Benefits - Expected Pension Benefit Payments for Succeeding Fiscal Years (Details) $ in Millions	Sep. 30, 2023 USD ($)
Pension Plan [Member]
2024	$ 52.4
2025	45.3
2026	41.8
2027	41.8
2028	43.3
2029-2032	202.8
Pension Plan [Member] \| Spire Missouri [Member]
2024	41.0
2025	34.1
2026	30.4
2027	29.4
2028	30.5
2029-2032	139.1
Pension Plan [Member] \| Spire Alabama Inc [Member]
2024	8.0
2025	7.7
2026	7.8
2027	8.7
2028	8.9
2029-2032	44.1
Other Postretirement Benefits Plan [Member]
2024	14.6
2025	14.8
2026	14.9
2027	14.8
2028	14.5
2029-2032	68.6
Other Postretirement Benefits Plan [Member] \| Spire Missouri [Member]
2024	11.6
2025	11.8
2026	11.8
2027	11.7
2028	11.4
Other Postretirement Benefits Plan [Member] \| Spire Alabama Inc [Member]
2024	2.9
2025	2.9
2026	2.9
2027	2.9
2028	$ 2.9

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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Amount of benefit for defined benefit plan expected to be paid in next fiscal year following current fiscal year.

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