PENSION PLANS AND OTHER POSTRETIREMENT BENEFITS - Projected Benefit Obligation (Details) - USD ($) $ in Millions	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 794.8	$ 652.3
Accumulated benefit obligation	724.5	591.4
Fair value of plan assets	540.5	448.9
Laclede Gas
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	560.0	497.6
Accumulated benefit obligation	517.7	456.9
Fair value of plan assets	395.7	339.9
Alagasco
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	174.3	154.7
Accumulated benefit obligation	149.8	134.5
Fair value of plan assets	$ 100.0	$ 109.0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

If aggregate disclosures are presented, the aggregate pension accumulated benefit obligation for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=73719040&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2417-114920

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If aggregate disclosures are presented, the aggregate fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

+ References

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- Definition

If aggregate disclosures are presented, the aggregate benefit obligation for plans with benefit obligations in excess of plan assets as of the measurement date of each statement of financial position presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2417-114920

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