Pension Plans and Other Postretirement Benefits - Expected Future Benefit Payments (Details) $ in Millions	Sep. 30, 2019 USD ($)
Pension Plans
Expected benefit payments [Abstract]
2020	$ 72.6
2021	64.3
2022	58.8
2023	58.7
2024	57.5
2025- 2029	268.3
Pension Plans \| Spire Missouri
Expected benefit payments [Abstract]
2020	56.1
2021	47.8
2022	42.6
2023	42.7
2024	41.3
2025- 2029	190.1
Pension Plans \| Spire Alabama
Expected benefit payments [Abstract]
2020	13.6
2021	13.5
2022	13.2
2023	12.8
2024	13.0
2025- 2029	60.6
Other Postretirement Plans
Expected benefit payments [Abstract]
2020	13.6
2021	14.0
2022	14.5
2023	14.8
2024	15.0
2025- 2029	73.0
Other Postretirement Plans \| Spire Missouri
Expected benefit payments [Abstract]
2020	10.6
2021	11.0
2022	11.4
2023	11.7
2024	11.8
2025- 2029	57.1
Other Postretirement Plans \| Spire Alabama
Expected benefit payments [Abstract]
2020	2.7
2021	2.7
2022	2.8
2023	2.8
2024	2.8
2025- 2029	$ 13.5

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

+ References

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

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

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

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