REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 414.6	$ 373.9
Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	121.3	117.0
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	277.7	240.9
Compensated absences
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	8.2	8.2
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	7.4	7.8
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	414.6	373.9
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	121.3	117.0
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	277.7	240.9
Laclede Gas | Compensated absences
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	8.2	8.2
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 7.4	$ 7.8