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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Inter-company Transactions (Details) - Affiliated Entity - Spire Missouri - USD ($) $ in Millions | 3 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Spire Marketing | Regulated Operation |  |
Related Party Transaction [Line Items] |  |
Purchases of natural gas from Spire Marketing | $ 22.3 | $ 20.5
Sales of natural gas to Spire Marketing | 0.1 | 3.6
Spire NGL Inc. | Unregulated Operation |  |
Related Party Transaction [Line Items] |  |
Transportation services received from Spire NGL Inc. | $ 0.3 | $ 0.3

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- Definition Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864 + Details
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- Definition Purchases during the period (excluding transactions that are eliminated in consolidated or combined financial statements) with related party. + References No definition available. + Details
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- Definition 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. + References 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=63488584&loc=d3e20235-122688 Reference 2: 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 + Details
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- Details
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- Details
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