DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Fair Value of Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	$ 7.7	[1]	$ 6.3	[1]
Fair value of liability derivatives presented above	12.0	[1]	10.6	[1]
Gas Utility | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	2.5	[1]	1.7	[1]
Fair value of liability derivatives presented above	9.3	[1]	8.9	[1]
Gas Utility | Gasoline and heating oil contracts | Designated as Hedging Instrument | Accounts Receivable – Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0	[1]	0.1	[1]
Fair value of liability derivatives presented above	0.2	[1]	0	[1]
Gas Utility | Gasoline and heating oil contracts | Not Designated as Hedging Instrument | Accounts Receivable – Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0	[1]
Fair value of liability derivatives presented above	0.4	[1]
Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Accounts Receivable – Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	2.4	[1]	1.5	[1]
Fair value of liability derivatives presented above	5.2	[1]	3.5	[1]
Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Prepayments and other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0	[1]	0	[1]
Fair value of liability derivatives presented above	0	[1]	0	[1]
Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Derivative Asset Instruments
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0.1	[1]
Fair value of liability derivatives presented above	3.7	[1]
Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Deferred Charges - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above			0	[1]
Fair value of liability derivatives presented above			0	[1]
Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Current Liabilities - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above			0.2	[1]
Fair value of liability derivatives presented above			4.0	[1]
Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Deferred Credits and Other Liabilities - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above			0	[1]
Fair value of liability derivatives presented above			1.4	[1]
Gas Marketing | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	1.4	[1]	2.3	[1]
Fair value of liability derivatives presented above	0.8	[1]	0.5	[1]
Gas Marketing | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	3.8	[1]	2.3	[1]
Fair value of liability derivatives presented above	1.9	[1]	1.2	[1]
Gas Marketing | Natural gas contracts | Designated as Hedging Instrument | Prepayments and other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0	[1]	2.2	[1]
Fair value of liability derivatives presented above	0	[1]	0.5	[1]
Gas Marketing | Natural gas contracts | Designated as Hedging Instrument | Derivative Asset Instruments
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0.7	[1]
Fair value of liability derivatives presented above	0.4	[1]
Gas Marketing | Natural gas contracts | Designated as Hedging Instrument | Deferred Charges - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0.7	[1]	0	[1]
Fair value of liability derivatives presented above	0.2	[1]	0	[1]
Gas Marketing | Natural gas contracts | Not Designated as Hedging Instrument | Accounts Receivable – Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above			0	[1]
Fair value of liability derivatives presented above			0	[1]
Gas Marketing | Natural gas contracts | Not Designated as Hedging Instrument | Prepayments and other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0	[1]	1.9	[1]
Fair value of liability derivatives presented above	0	[1]	0.2	[1]
Gas Marketing | Natural gas contracts | Not Designated as Hedging Instrument | Derivative Asset Instruments
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	3.5	[1]
Fair value of liability derivatives presented above	1.4	[1]
Gas Marketing | Natural gas contracts | Not Designated as Hedging Instrument | Deferred Charges - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0.3	[1]	0.1	[1]
Fair value of liability derivatives presented above	0	[1]	0.1	[1]
Gas Marketing | Natural gas contracts | Not Designated as Hedging Instrument | Current Liabilities - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0	[1]	0.3	[1]
Fair value of liability derivatives presented above	0.5	[1]	0.8	[1]
Gas Marketing | Natural gas contracts | Not Designated as Hedging Instrument | Deferred Credits and Other Liabilities - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0	[1]	0	[1]
Fair value of liability derivatives presented above	0	[1]	0.1	[1]
Laclede Gas
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	2.5		1.8
Fair value of liability derivatives presented above	9.5		8.9
Laclede Gas | Gas Utility
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	2.5		1.8
Fair value of liability derivatives presented above	9.5		8.9
Laclede Gas | Gas Utility | Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0		0.1
Fair value of liability derivatives presented above	0.2		0
Laclede Gas | Gas Utility | Not Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	2.5		1.7
Fair value of liability derivatives presented above	9.3		8.9
Laclede Gas | Gas Utility | Gasoline and heating oil contracts | Designated as Hedging Instrument | Accounts Receivable – Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0		0.1
Fair value of liability derivatives presented above	0.2		0
Laclede Gas | Gas Utility | Gasoline and heating oil contracts | Not Designated as Hedging Instrument | Accounts Receivable – Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0
Fair value of liability derivatives presented above	0.4
Laclede Gas | Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Accounts Receivable – Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	2.4		1.5
Fair value of liability derivatives presented above	5.2		3.5
Laclede Gas | Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Prepayments and other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0		0
Fair value of liability derivatives presented above	0		0
Laclede Gas | Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Derivative Asset Instruments
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0.1
Fair value of liability derivatives presented above	3.7
Laclede Gas | Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Deferred Charges - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above	0	[1]	0
Fair value of liability derivatives presented above	0	[1]	0
Laclede Gas | Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Current Liabilities - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above			0.2
Fair value of liability derivatives presented above			4.0
Laclede Gas | Gas Utility | Natural gas contracts | Not Designated as Hedging Instrument | Deferred Credits and Other Liabilities - Other
Derivatives, Fair Value [Line Items]
Fair value of asset derivatives presented above			0
Fair value of liability derivatives presented above			$ 1.4

[1] The fair values of Asset Derivatives and Liability Derivatives exclude the fair value of cash margin receivables or payables with counterparties subject to netting arrangements. Fair value amounts of derivative contracts (including the fair value amounts of cash margin receivables and payables) for which there is a legal right to set off are presented net on the Consolidated Balance Sheets. As such, the gross balances presented in the table above are not indicative of the Company’s net economic exposure. Refer to Note 9, Fair Value Measurements, to the Financial Statements for information on the valuation of derivative instruments.