COMMITMENTS AND CONTINGENCIES - Commitments (Details) $ in Millions	3 Months Ended
	Dec. 31, 2015 USD ($)
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 1,144.0
Laclede Gas
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	516.4
Alagasco
Long-term Purchase Commitment [Line Items]
Minimum total payments required for natural gas contracts	$ 365.0