REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) - USD ($) $ in Millions	Jun. 30, 2015	Sep. 30, 2014
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 366.1	$ 373.9
Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	130.3	117.0
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	221.2	240.9
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	14.6	16.0
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	366.1	373.9
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	130.3	117.0
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	221.2	240.9
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 14.6	$ 16.0