FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 16.1	$ 53.0	$ 27.5	$ 43.3
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	16.1	53.0
Short-term debt	287.1	74.0
Long-term debt, including current portion	1,851.0	912.7
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	16.1	53.0
Short-term debt	287.1	74.0
Long-term debt, including current portion	1,937.3	954.1
Laclede Gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3.7	23.9	2.4	0.9
Laclede Gas | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3.7	23.9
Short-term debt	238.6	120.7
Long-term debt, including current portion	807.9	887.7
Laclede Gas | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3.7	23.9
Short-term debt	238.6	120.7
Long-term debt, including current portion	876.2	930.4
Quoted Prices in Active Markets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	16.1	52.8
Short-term debt	0	0
Long-term debt, including current portion	0	0
Quoted Prices in Active Markets (Level 1) | Laclede Gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	3.7	23.9
Short-term debt	0	0
Long-term debt, including current portion	0	0
Significant Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0.2
Short-term debt	287.1	74.0
Long-term debt, including current portion	1,937.3	954.1
Significant Observable Inputs (Level 2) | Laclede Gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Short-term debt	238.6	120.7
Long-term debt, including current portion	876.2	930.4
Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Short-term debt	0	0
Long-term debt, including current portion	0	0
Significant Unobservable Inputs (Level 3) | Laclede Gas
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Short-term debt	0	0
Long-term debt, including current portion	$ 0	$ 0