REGULATORY MATTERS - Schedule of Regulatory Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Regulatory Assets [Line Items]
Regulatory Assets, Current	$ 57.7	$ 17.5
Regulatory assets	637.4	545.9
Total Regulatory Assets	695.1	563.4
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	38.3	0
Regulatory liabilities	126.1	82.6
Total Regulatory Liabilities	167.1	85.5
Pension and postretirement benefit costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	19.8	0
Refundable negative salvage
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	13.3	0
Regulatory liabilities	26.8	0
Other
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	5.2	0
Unamortized investment tax credits
Regulatory Liabilities [Line Items]
Regulatory liabilities	2.7	2.9
Postretirement liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities	28.4	0
Accrued cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities	60.5	59.1
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities	10.4	23.5
Total Regulatory Liabilities (non-current)
Regulatory Liabilities [Line Items]
Regulatory liabilities	128.8	85.5
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Regulatory Assets, Current	1.3	0
Regulatory assets	451.6	381.4
Unamortized purchased gas adjustments
Regulatory Assets [Line Items]
Regulatory assets	54.0	17.5
Future income taxes due from customers
Regulatory Assets [Line Items]
Regulatory assets	117.0	112.9
Accrued cost of removal
Regulatory Assets [Line Items]
Regulatory assets	2.8	0
Accretion and depreciation of asset retirement obligations
Regulatory Assets [Line Items]
Regulatory assets	18.4	0
Enhanced stability reserve
Regulatory Assets [Line Items]
Regulatory assets	3.3	0
Purchased gas costs
Regulatory Assets [Line Items]
Regulatory assets	4.3	18.2
Compensated absences
Regulatory Assets [Line Items]
Regulatory assets	8.2	8.0
Other
Regulatory Assets [Line Items]
Regulatory Assets, Current	2.4	0
Regulatory assets	31.8	25.4
Sub Total Regulatory Assets (non-current)
Regulatory Assets [Line Items]
Regulatory assets	637.4	545.9
Laclede Gas
Regulatory Assets [Line Items]
Regulatory Assets, Current	54.0	17.5
Regulatory assets	541.7	545.9
Total Regulatory Assets	595.7	563.4
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory liabilities	70.0	61.9
Total Regulatory Liabilities	72.7	64.8
Laclede Gas | Pension and postretirement benefit costs
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	0	0
Laclede Gas | Refundable negative salvage
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	0	0
Regulatory liabilities	0	0
Laclede Gas | Other
Regulatory Liabilities [Line Items]
Regulatory Liability, Current	0	0
Laclede Gas | Unamortized investment tax credits
Regulatory Liabilities [Line Items]
Regulatory liabilities	2.7	2.9
Laclede Gas | Postretirement liabilities
Regulatory Liabilities [Line Items]
Regulatory liabilities	0	0
Laclede Gas | Accrued cost of removal
Regulatory Liabilities [Line Items]
Regulatory liabilities	60.5	59.0
Laclede Gas | Other
Regulatory Liabilities [Line Items]
Regulatory liabilities	9.5	2.9
Laclede Gas | Total Regulatory Liabilities (non-current)
Regulatory Liabilities [Line Items]
Regulatory liabilities	72.7	64.8
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Regulatory Assets, Current	0	0
Regulatory assets	380.4	381.4
Laclede Gas | Unamortized purchased gas adjustments
Regulatory Assets [Line Items]
Regulatory assets	54.0	17.5
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Regulatory assets	117.0	112.9
Laclede Gas | Accrued cost of removal
Regulatory Assets [Line Items]
Regulatory assets	0	0
Laclede Gas | Accretion and depreciation of asset retirement obligations
Regulatory Assets [Line Items]
Regulatory assets	0	0
Laclede Gas | Enhanced stability reserve
Regulatory Assets [Line Items]
Regulatory assets	0	0
Laclede Gas | Purchased gas costs
Regulatory Assets [Line Items]
Regulatory assets	4.3	18.2
Laclede Gas | Compensated absences
Regulatory Assets [Line Items]
Regulatory assets	8.2	8.0
Laclede Gas | Other
Regulatory Assets [Line Items]
Regulatory Assets, Current	0	0
Regulatory assets	31.8	25.4
Laclede Gas | Sub Total Regulatory Assets (non-current)
Regulatory Assets [Line Items]
Regulatory assets	$ 541.7	$ 545.9