NOTES PAYABLE AND CREDIT AGREEMENTS - Spire Short-term Borrowings (Details) - USD ($)	1 Months Ended	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2016	Sep. 30, 2015
Short-term Debt [Line Items]
Weighted average borrowings outstanding		$ 273,900,000	$ 300,600,000
Weighted average interest rate		0.90%	0.70%
Minimum borrowing outstanding		$ 73,100,000	$ 180,100,000
Maximum borrowing outstanding		427,200,000	488,500,000
Short-term debt		$ 398,700,000	$ 338,000,000
Weighted average interest rate		1.10%	0.80%
Line of Credit
Short-term Debt [Line Items]
Minimum borrowing outstanding		$ 0	$ 32,500,000
Maximum borrowing outstanding		82,000,000	80,000,000
Laclede Gas
Short-term Debt [Line Items]
Weighted average borrowings outstanding		$ 215,700,000	$ 213,000,000
Weighted average interest rate		0.70%	0.40%
Minimum borrowing outstanding		$ 127,800,000.0	$ 104,200,000.0
Maximum borrowing outstanding		307,200,000.0	341,000,000
Short-term debt		$ 243,700,000	$ 233,000,000
Weighted average interest rate		0.80%	0.50%
Laclede Gas | Commercial Paper
Short-term Debt [Line Items]
Weighted average borrowings outstanding		$ 201,000,000	$ 212,700,000
Weighted average interest rate		0.70%	0.40%
Minimum borrowing outstanding		$ 43,000,000	$ 102,100,000.0
Maximum borrowing outstanding		307,200,000.0	341,000,000
Short-term debt		$ 243,700,000	$ 233,000,000
Weighted average interest rate		0.80%	0.50%
Spire | Line of Credit
Short-term Debt [Line Items]
Weighted average borrowings outstanding		$ 42,700,000	$ 65,600,000
Weighted average interest rate		1.60%	1.40%
Short-term debt		$ 73,000,000	$ 74,000,000
Weighted average interest rate		1.80%	1.50%
Alagasco
Short-term Debt [Line Items]
Weighted average borrowings outstanding		$ 42,600,000	$ 22,300,000
Weighted average interest rate		1.40%	1.10%
Minimum borrowing outstanding		$ 19,000,000	$ 0
Maximum borrowing outstanding		82,000,000	69,500,000
Short-term debt		$ 82,000,000	$ 31,000,000
Weighted average interest rate		1.50%	1.20%
Alagasco | Line of Credit
Short-term Debt [Line Items]
Weighted average borrowings outstanding	$ 22,300,000	$ 30,200,000	$ 22,300,000
Weighted average interest rate	1.10%	1.40%	1.10%
Minimum borrowing outstanding		$ 0	$ 0
Maximum borrowing outstanding		82,000,000	69,500,000.0
Short-term debt		$ 82,000,000	$ 31,000,000
Weighted average interest rate		1.50%	1.20%