DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Derivative Instruments Reconciliation (Details) - USD ($) $ in Millions	Sep. 30, 2016	Sep. 30, 2015
Offsetting Derivative Assets [Abstract]
Fair value of asset derivatives presented above	$ 18.4	$ 13.5
Fair value of cash margin receivables offset with derivatives	2.5	13.9
Netting of assets and liabilities with the same counterparty	(7.6)	(22.2)
Derivative asset after the effects of netting	13.3	5.2
Derivative instrument assets	11.4	4.6
Deferred Charges – Other	1.9	0.6
Offsetting Derivative Liabilities [Abstract]
Fair value of liability derivatives presented above	12.5	29.8
Netting of assets and liabilities with the same counterparty	(7.6)	(22.2)
Derivative liability after the effects of netting	4.9	7.6
Current Liabilities – Other	4.8	6.8
Deferred Credits – Other	0.1	0.8
Laclede Gas
Offsetting Derivative Assets [Abstract]
Fair value of asset derivatives presented above	5.7	1.2
Fair value of cash margin receivables offset with derivatives	0.8	15.5
Netting of assets and liabilities with the same counterparty	(1.6)	(16.7)
Derivative asset after the effects of netting	4.9	0.0
Derivative instrument assets	4.9	0.0
Offsetting Derivative Liabilities [Abstract]
Fair value of liability derivatives presented above	1.8	22.6
Netting of assets and liabilities with the same counterparty	(1.6)	(16.7)
Derivative liability after the effects of netting	0.2	5.9
Current Liabilities – Other	0.2	5.7
Deferred Credits – Other	$ 0.0	$ 0.2