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PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Expected Future Benefit Payments (Details) $ in Millions | Sep. 30, 2017 USD ($)
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Pension Plans |
Expected benefit payments [Abstract] |
2017 | $ 63.5
2018 | 63.2
2019 | 63.2
2020 | 58.1
2021 | 57.9
2022 - 2026 | 281.1
Postretirement Plans |
Expected benefit payments [Abstract] |
2017 | 15.0
2018 | 16.0
2019 | 17.1
2020 | 18.3
2021 | 18.9
2022 - 2026 | 101.3
Spire Missouri | Pension Plans |
Expected benefit payments [Abstract] |
2017 | 50.7
2018 | 49.5
2019 | 49.1
2020 | 43.5
2021 | 42.1
2022 - 2026 | 198.1
Spire Missouri | Postretirement Plans |
Expected benefit payments [Abstract] |
2017 | 11.8
2018 | 12.8
2019 | 14.0
2020 | 15.2
2021 | 15.9
2022 - 2026 | 86.5
Spire Alabama | Pension Plans |
Expected benefit payments [Abstract] |
2017 | 10.3
2018 | 11.1
2019 | 11.5
2020 | 11.9
2021 | 13.0
2022 - 2026 | 67.8
Spire Alabama | Postretirement Plans |
Expected benefit payments [Abstract] |
2017 | 2.8
2018 | 2.8
2019 | 2.8
2020 | 2.8
2021 | 2.7
2022 - 2026 | $ 13.0

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