PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Expected Future Benefit Payments (Details) $ in Millions	Sep. 30, 2017 USD ($)
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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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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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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