STOCKHOLDERS' EQUITY - Schedule of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	$ (1.7)	$ (0.8)
Other comprehensive (loss) income	(0.3)	(0.9)
Balance, period end	(2.0)	(1.7)
Laclede Gas
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	(1.9)	(2.1)
Other comprehensive (loss) income	0.2	0.2
Balance, period end	(1.7)	(1.9)
Net Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	0.2	1.4
Other comprehensive (loss) income	(0.6)	(1.2)
Balance, period end	(0.4)	0.2
Net Unrealized Gains (Losses) on Cash Flow Hedges | Laclede Gas
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	0.0	0.1
Other comprehensive (loss) income	(0.2)	(0.1)
Balance, period end	(0.2)	0.0
Defined Benefit Pension and Other Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	(1.9)	(2.2)
Other comprehensive (loss) income	0.4	0.3
Balance, period end	(1.5)	(1.9)
Defined Benefit Pension and Other Postretirement Benefit Plans | Laclede Gas
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	(1.9)	(2.2)
Other comprehensive (loss) income	0.4	0.3
Balance, period end	(1.5)	(1.9)
Net Unrealized Losses on Available for Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	0.0	0.0
Other comprehensive (loss) income	(0.1)	0.0
Balance, period end	(0.1)	0.0
Net Unrealized Losses on Available for Sale Securities | Laclede Gas
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	0.0	0.0
Other comprehensive (loss) income	0.0	0.0
Balance, period end	$ 0.0	$ 0.0