Pension Plans and Other Postretirement Benefits - Expected Future Benefit Payments (Details) $ in Millions	Sep. 30, 2020 USD ($)
Pension Plans
Expected benefit payments [Abstract]
2021	$ 65.6
2022	64.1
2023	60.8
2024	58.6
2025	54.4
2026- 2030	246.0
Pension Plans \| Spire Missouri
Expected benefit payments [Abstract]
2021	49.1
2022	45.6
2023	43.3
2024	41.9
2025	37.7
2026- 2030	168.7
Pension Plans \| Spire Alabama
Expected benefit payments [Abstract]
2021	13.5
2022	15.4
2023	14.3
2024	13.5
2025	13.3
2026- 2030	59.0
Other Postretirement Plans
Expected benefit payments [Abstract]
2021	14.7
2022	15.4
2023	16.1
2024	16.5
2025	16.6
2026- 2030	78.2
Other Postretirement Plans \| Spire Missouri
Expected benefit payments [Abstract]
2021	11.7
2022	12.3
2023	12.9
2024	13.2
2025	13.3
2026- 2030	61.7
Other Postretirement Plans \| Spire Alabama
Expected benefit payments [Abstract]
2021	2.7
2022	2.8
2023	2.9
2024	3.0
2025	3.0
2026- 2030	$ 14.2

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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=118255775&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 fifth 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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