COMMITMENTS AND CONTINGENCIES - Commitments (Details) $ in Millions	12 Months Ended
Sep. 30, 2018 USD ($)
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 1,240.9
Outstanding mortgage loans incurred in connection with various real estate ventures with general partners	1.3
Spire Missouri
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	572.4
Spire Missouri \| Purchase Commitment \| Subsidiary of Common Parent
Long-term Purchase Commitment [Line Items]
Annual purchase commitment	$ 1.0
Commitment termination minimum required notification period	6 months
Spire Alabama
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 286.5

Purchase Commitment, Termination, Minimum Notification Period Required

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The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

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Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

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Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

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