COMMITMENTS AND CONTINGENCIES - Commitments (Details) $ in Millions	9 Months Ended
	Jun. 30, 2015 USD ($)
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 1,468.0
Laclede Gas
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	699.9
Alagasco
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 482.9