REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) - USD ($) $ in Millions	Sep. 30, 2016	Sep. 30, 2015
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 404.8	$ 372.4
Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	151.3	134.5
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	240.6	223.7
Compensated absences
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	0.0	0.0
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	12.9	14.2
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	404.8	372.4
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	151.3	134.5
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	240.6	223.7
Laclede Gas | Compensated absences
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	0.0	0.0
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 12.9	$ 14.2