Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(e))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Related Parties

-URI http://asc.fasb.org/extlink&oid=16382449

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.6-07.1(c))

-URI http://asc.fasb.org/extlink&oid=6488393&loc=d3e606610-122999

Name:	us-gaap_RevenueFromRelatedParties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Transactions with Affiliates (Details) - Affiliated Entity - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Alagasco
Related Party Transaction [Line Items]
Employee-related integration transactions costs	$ 2.8
Laclede Gas \| Regulated Operation \| Laclede Energy Resources
Related Party Transaction [Line Items]
Revenue from related parties	4.0	$ 5.1	$ 10.4
Laclede Gas \| Unregulated Operation \| Laclede Venture Corporation
Related Party Transaction [Line Items]
Revenue from related parties	0.1	0.0	0.0
Laclede Energy Resources \| Regulated Operation \| Laclede Gas
Related Party Transaction [Line Items]
Revenue from related parties	74.1	89.1	34.6
Laclede Pipeline Company \| Unregulated Operation \| Laclede Gas
Related Party Transaction [Line Items]
Revenue from related parties	1.0	1.0	1.0
Laclede Risk Services \| Regulated Operation \| Laclede Gas
Related Party Transaction [Line Items]
Revenue from related parties	$ 1.0	$ 0.6	$ 0.7