FINANCING ARRANGEMENTS (Details)		3 Months Ended
	Dec. 14, 2016 USD ($) bank borrower agreement	Dec. 31, 2016
Line of Credit Facility [Line Items]
Number of terminated loan agreements | agreement	3
Debt covenant, short-term debt to capital requirement, maximum	70.00%
Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Number of banks in loan agreement | bank	11
Maximum borrowing capacity	$ 975,000,000.0
Number of borrowers under loan agreement | borrower	3
Line of Credit | Revolving Credit Facility | Spire
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 300,000,000.0
Ratio of short-term debt to total capital		0.59
Line of Credit | Revolving Credit Facility | Laclede Gas
Line of Credit Facility [Line Items]
Maximum borrowing capacity	475,000,000.0
Ratio of short-term debt to total capital		0.51
Line of Credit | Revolving Credit Facility | Alagasco
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 200,000,000.0
Ratio of short-term debt to total capital		0.29
Line of Credit | Revolving Credit Facility | Credit Availability Concentration Risk
Line of Credit Facility [Line Items]
Concentration risk		12.30%