STOCKHOLDER'S EQUITY - Schedule of Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	$ (0.8)	$ (4.1)
Current-period change	(0.9)	3.3
Balance, period end	(1.7)	(0.8)
Net Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	1.4	(1.9)
Current-period change	(1.2)	3.3
Balance, period end	0.2	1.4
Defined Benefit Pension and Other Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	(2.2)	(2.2)
Current-period change	0.3	0
Balance, period end	(1.9)	(2.2)
Laclede Gas
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	(2.1)	(2.1)
Current-period change	0.2	0
Balance, period end	(1.9)	(2.1)
Laclede Gas | Net Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	0.1	0.1
Current-period change	(0.1)	0
Balance, period end	0	0.1
Laclede Gas | Defined Benefit Pension and Other Postretirement Benefit Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balance, beginning period	(2.2)	(2.2)
Current-period change	0.3	0
Balance, period end	$ (1.9)	$ (2.2)