REGULATORY MATTERS - Schedule of Regulatory Assets Not Earnings a Return (Details) - USD ($) $ in Millions	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 369.9	$ 372.4	$ 414.6
Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	138.7	134.5	121.3
Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	217.7	223.7	277.7
Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	13.5	14.2	15.6
Laclede Gas
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	369.9	372.4	414.6
Laclede Gas | Future income taxes due from customers
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	138.7	134.5	121.3
Laclede Gas | Pension and postretirement benefit costs
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	217.7	223.7	277.7
Laclede Gas | Other
Regulatory Assets [Line Items]
Total Regulatory Assets Not Earning a Return	$ 13.5	$ 14.2	$ 15.6