REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) - USD ($) $ in Millions	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 399.1	$ 404.8	$ 369.9
Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	155.5	151.3	138.7
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	231.4	240.6	217.7
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	12.2	12.9	13.5
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	399.1	404.8	369.9
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	155.5	151.3	138.7
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	231.4	240.6	217.7
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 12.2	$ 12.9	$ 13.5