FINANCING ARRANGEMENTS AND LONG-TERM DEBT (Details) $ / shares in Units, shares in Millions					3 Months Ended	6 Months Ended		12 Months Ended
	Apr. 03, 2017 USD ($) $ / shares shares	Feb. 22, 2017 USD ($)	Dec. 14, 2016 USD ($) agreement bank borrower	Jun. 11, 2014 USD ($) $ / shares	Dec. 31, 2016	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2014 equity_units	Mar. 15, 2017 USD ($)	Mar. 10, 2017 USD ($)	Jun. 30, 2014 $ / shares
Line of Credit Facility [Line Items]
Number of terminated loan agreements | agreement			3
Debt covenant, short-term debt to capital requirement, maximum			70.00%
Corporate units, stated value per unit (usd per share) | $ / shares											$ 50
Laclede Gas
Line of Credit Facility [Line Items]
Repayment of short-term debt - net						$ 243,700,000	$ 63,400,000
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
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					0.57
Line of Credit | Revolving Credit Facility | Laclede Gas
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 475,000,000.0
Number of borrowers under loan agreement | borrower			3
Ratio of short-term debt to total capital					0.49
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%
Senior Notes
Line of Credit Facility [Line Items]
Maximum aggregate face amount		$ 6,200,000.0
Proceeds from issuance of debt		150,000,000.0
Notes Payable
Line of Credit Facility [Line Items]
Debt instrument, repurchase amount										$ 250,000,000.0
Alagasco
Line of Credit Facility [Line Items]
Number of equity instruments | equity_units								2,875,000
Corporate units, stated value per unit (usd per share) | $ / shares				$ 50
Interest rate (percentage)				2.00%
Alagasco | Junior Subordinated Debt
Line of Credit Facility [Line Items]
Proceeds from debt				$ 143,800,000
Senor Notes Due in 2024 | Senior Notes
Line of Credit Facility [Line Items]
Maximum aggregate face amount		$ 143,800,000.0
Interest rate (percentage)		3.543%
Senior Notes Due March15, 2027 | Senior Notes
Line of Credit Facility [Line Items]
Maximum aggregate face amount									$ 100,000,000.0
Interest rate (percentage)									3.93%
Subsequent Event
Line of Credit Facility [Line Items]
Common stock, issued (in shares) | shares	2.5
Shares issued, price per share (usd per share) | $ / shares	$ 57.3921
Conversion to common stock, rate per share (percentage)	0.8712
Repayment of short-term debt - net	$ 142,000,000