SUBSEQUENT EVENTS (Details) $ / shares in Units, $ in Millions			6 Months Ended
	Apr. 11, 2017 USD ($)	Apr. 03, 2017 USD ($) equity_units $ / shares shares	Mar. 31, 2017 USD ($) shares	Mar. 31, 2016 USD ($) shares	Sep. 30, 2016 shares	Jun. 30, 2014 $ / shares
Subsequent Event [Line Items]
Common stock, issued (in shares) | shares			45,700,000	43,400,000	45,600,000
Corporate units, stated value per unit (usd per share) | $ / shares						$ 50
Subsequent Event
Subsequent Event [Line Items]
Common stock, issued (in shares) | shares		2,500,000.0
Shares issued, price per share (usd per share) | $ / shares		$ 57.3921
Price per share, paid for fractional shares (usd per share) | $ / shares		$ 67.50
Conversion to common stock, rate per share (percentage)		0.8712
Repayment of short-term debt - net		$ 142.0
Laclede Gas
Subsequent Event [Line Items]
Common stock, issued (in shares) | shares			24,577	24,577	24,577
Repayment of short-term debt - net			$ 243.7	$ 63.4
Laclede Gas | Eastern Missouri service | Subsequent Event
Subsequent Event [Line Items]
Public Utilities, requested rate increase (decrease), amount	$ 28.5
Laclede Gas | Western Missouri Service | Subsequent Event
Subsequent Event [Line Items]
Public Utilities, requested rate increase (decrease), amount	$ 37.0
Securities Subject to Mandatory Redemption [Member] | Subsequent Event
Subsequent Event [Line Items]
Number of equity instruments | equity_units		2,875,000