REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) - USD ($) $ in Millions	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2016
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 412.5	$ 404.8	$ 367.4
Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	159.7	151.3	142.3
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	241.0	240.6	211.5
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	11.8	12.9	13.6
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	412.5	404.8	367.4
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	159.7	151.3	142.3
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	241.0	240.6	211.5
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 11.8	$ 12.9	$ 13.6