REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 445.1	$ 388.4
Deferred Tax Asset [Domain]
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	117.0	112.9
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	312.1	259.9
Compensated absences
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	8.2	8.0
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	7.8	7.6
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	373.9	388.4
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	117.0	112.9
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	240.9	259.9
Laclede Gas | Compensated absences
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	8.2	8.0
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 7.8	$ 7.6