PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Expected Future Benefit Payments (Details) $ in Millions	Sep. 30, 2016 USD ($)
Pension Plans
Expected benefit payments [Abstract]
2017	$ 61.3
2018	56.2
2019	57.1
2020	56.6
2021	56.8
2022 - 2026	286.3
Postretirement Plans
Expected benefit payments [Abstract]
2017	15.4
2018	16.7
2019	17.9
2020	19.1
2021	20.1
2022 - 2026	108.6
Laclede Gas \| Pension Plans
Expected benefit payments [Abstract]
2017	48.2
2018	43.3
2019	43.5
2020	42.2
2021	40.4
2022 - 2026	196.6
Laclede Gas \| Postretirement Plans
Expected benefit payments [Abstract]
2017	12.3
2018	13.7
2019	14.8
2020	15.8
2021	16.8
2022 - 2026	92.5
Alagasco \| Pension Plans
Expected benefit payments [Abstract]
2017	10.9
2018	10.6
2019	11.2
2020	11.9
2021	13.7
2022 - 2026	74.5
Alagasco \| Postretirement Plans
Expected benefit payments [Abstract]
2017	2.9
2018	2.8
2019	2.8
2020	2.9
2021	2.9
2022 - 2026	$ 14.1

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the five fiscal years after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ 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=65897934&loc=d3e1928-114920

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- Definition

Amount of benefits from a defined benefit plan expected to be paid in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of benefits from a defined benefit plan expected to be paid in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of benefits from a defined benefit plan expected to be paid in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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