REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 373.1	$ 373.9
Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	125.6	117.0
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	232.3	240.9
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	15.2	16.0
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	373.1	373.9
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	125.6	117.0
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	232.3	240.9
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 15.2	$ 16.0