FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2013	Jun. 30, 2013	Sep. 30, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 571.8	$ 53.0	$ 556.5	$ 27.5
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	571.8	53.0
Short-term debt	0	74.0
Long-term debt, including current portion	976.6	912.7
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	571.8	53.0
Short-term debt	0	74.0
Long-term debt, including current portion	1,044.0	954.1
Laclede Gas Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6.0	23.9	28.8	2.4
Laclede Gas Company | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6.0	23.9
Short-term debt	126.9	120.7
Long-term debt, including current portion	807.9	887.7
Laclede Gas Company | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6.0	23.9
Short-term debt	126.9	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	250.4	52.8
Short-term debt	0	0
Long-term debt, including current portion	0	0
Quoted Prices in Active Markets (Level 1) | Laclede Gas Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	6.0	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	321.4	0.2
Short-term debt	0	74.0
Long-term debt, including current portion	1,044.0	954.1
Significant Observable Inputs (Level 2) | Laclede Gas Company
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Short-term debt	126.9	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 Company
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