DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES - Exchange-Traded/Cleared Derivatives (Details)	Sep. 30, 2014 MMBTU
Laclede Gas
Derivative [Line Items]
MMBtu (millions)	21,000,000
Avg. Price Per MMBtu	2.60
Natural gas contracts | Fiscal 2015 | Laclede Gas | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
Natural gas contracts | Fiscal 2015 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	8,010,000
Avg. Price Per MMBtu	3.99
Natural gas contracts | Fiscal 2015 | Laclede Energy Resources | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	4,200,000
Avg. Price Per MMBtu	4.37
Natural gas contracts | Fiscal 2015 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	6,970,000
Avg. Price Per MMBtu	4.14
Natural gas contracts | Fiscal 2016 | Laclede Gas | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
Natural gas contracts | Fiscal 2016 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	940,000
Avg. Price Per MMBtu	3.92
Natural gas contracts | Fiscal 2016 | Laclede Energy Resources | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	2,220,000
Avg. Price Per MMBtu	4.26
Natural gas contracts | Fiscal 2016 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	530,000
Avg. Price Per MMBtu	4.07
Natural gas contracts | Fiscal 2017 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
Natural gas contracts | Fiscal 2017 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	40,000
Avg. Price Per MMBtu	4.24
Natural gas contracts | Fiscal 2018 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
Natural gas contracts | Fiscal 2018 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	10,000
Avg. Price Per MMBtu	4.27
ICE Open long basis swap positions | Fiscal 2015 | Laclede Gas | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
ICE Open long basis swap positions | Fiscal 2015 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
ICE Open long basis swap positions | Fiscal 2015 | Laclede Energy Resources | Open Short Futures Positions
Derivative [Line Items]
MMBtu (millions)	1,440,000
Avg. Price Per MMBtu	0.13
ICE Open long basis swap positions | Fiscal 2015 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	1,160,000
Avg. Price Per MMBtu	0.38
ICE Open long basis swap positions | Fiscal 2016 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
ICE Open long basis swap positions | Fiscal 2016 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	2,750,000
Avg. Price Per MMBtu	0.58
ICE Open long basis swap positions | Fiscal 2017 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
ICE Open long basis swap positions | Fiscal 2017 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	6,870,000
Avg. Price Per MMBtu	0.50
ICE Open long basis swap positions | Fiscal 2018 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
ICE Open long basis swap positions | Fiscal 2018 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	1,090,000
Avg. Price Per MMBtu	0.50
OTC Open long futures/swap positions | Fiscal 2015 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	16,430,000
Avg. Price Per MMBtu	4.28
OTC Open long futures/swap positions | Fiscal 2015 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00
OTC Open long futures/swap positions | Fiscal 2016 | Laclede Gas | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	2,690,000
Avg. Price Per MMBtu	4.22
OTC Open long futures/swap positions | Fiscal 2016 | Laclede Energy Resources | Open Long Futures Positions
Derivative [Line Items]
MMBtu (millions)	0
Avg. Price Per MMBtu	0.00