PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Expected Future Benefit Payments (Details) $ in Millions	Sep. 30, 2015 USD ($)
Pension Plans \| Pensions/Benefits from Qualified Trust
Expected benefit payments [Abstract]
2016	$ 45.9
2017	45.7
2018	43.5
2019	44.9
2020	46.4
2021 - 2025	235.0
Pension Plans \| Pensions/Benefits from Funds
Expected benefit payments [Abstract]
2016	0.5
2017	0.6
2018	0.5
2019	0.4
2020	0.5
2021 - 2025	2.1
Postretirement Plans \| Pensions/Benefits from Qualified Trust
Expected benefit payments [Abstract]
2016	15.1
2017	16.2
2018	17.5
2019	18.3
2020	19.2
2021 - 2025	104.9
Laclede Gas \| Pension Plans \| Pensions/Benefits from Qualified Trust
Expected benefit payments [Abstract]
2016	36.4
2017	35.7
2018	33.9
2019	35.0
2020	35.4
2021 - 2025	177.3
Laclede Gas \| Pension Plans \| Pensions/Benefits from Funds
Expected benefit payments [Abstract]
2016	0.5
2017	0.6
2018	0.5
2019	0.4
2020	0.5
2021 - 2025	2.1
Laclede Gas \| Postretirement Plans \| Pensions/Benefits from Qualified Trust
Expected benefit payments [Abstract]
2016	12.3
2017	13.3
2018	14.6
2019	15.4
2020	16.3
2021 - 2025	90.4
Laclede Gas \| Postretirement Plans \| Pensions/Benefits from Funds
Expected benefit payments [Abstract]
2016	0.4
2017	0.4
2018	0.4
2019	0.4
2020	0.4
2021 - 2025	2.3
Alagasco \| Pension Plans \| Pensions/Benefits from Qualified Trust
Expected benefit payments [Abstract]
2016	9.5
2017	10.0
2018	9.6
2019	9.9
2020	11.0
2021 - 2025	57.7
Alagasco \| Postretirement Plans \| Pensions/Benefits from Qualified Trust
Expected benefit payments [Abstract]
2016	2.8
2017	2.9
2018	2.9
2019	2.9
2020	2.9
2021 - 2025	$ 14.5

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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=58740216&loc=d3e1928-114920

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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 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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