Pension Plans and Other Postretirement Benefits - Expected Future Benefit Payments (Details) $ in Millions	Sep. 30, 2021 USD ($)
Pension Plans
Expected benefit payments [Abstract]
2022	$ 64.3
2023	59.2
2024	57.8
2025	52.4
2026	50.6
2027- 2031	236.8
Pension Plans \| Spire Missouri
Expected benefit payments [Abstract]
2022	46.6
2023	42.2
2024	41.9
2025	36.9
2026	34.9
2027- 2031	164.3
Pension Plans \| Spire Alabama
Expected benefit payments [Abstract]
2022	14.7
2023	13.9
2024	12.7
2025	12.2
2026	12.3
2027- 2031	54.0
Other Postretirement Plans
Expected benefit payments [Abstract]
2022	14.1
2023	14.9
2024	15.6
2025	15.9
2026	15.8
2027- 2031	76.1
Other Postretirement Plans \| Spire Missouri
Expected benefit payments [Abstract]
2022	11.2
2023	11.9
2024	12.5
2025	12.7
2026	12.7
2027- 2031	59.9
Other Postretirement Plans \| Spire Alabama
Expected benefit payments [Abstract]
2022	2.7
2023	2.8
2024	2.9
2025	2.9
2026	2.9
2027- 2031	$ 14.3

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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

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

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