COMMITMENTS AND CONTINGENCIES - Commitments (Details) $ in Millions	3 Months Ended
	Dec. 31, 2016 USD ($)
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 1,463.4
Laclede Gas
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	614.8
Alagasco
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 340.0