REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) - USD ($) $ in Millions	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 363.4	$ 372.4	$ 366.1
Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	146.4	134.5	130.3
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	203.8	223.7	221.2
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	13.2	14.2	14.6
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	363.4	372.4	366.1
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	146.4	134.5	130.3
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	203.8	223.7	221.2
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 13.2	$ 14.2	$ 14.6