COMMITMENTS AND CONTINGENCIES - Leases and Guarantees (Details) (USD $) In Millions, unless otherwise specified		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2014 Laclede Gas	Sep. 30, 2013 Laclede Gas	Sep. 30, 2012 Laclede Gas	Sep. 30, 2014 Missouri Gas Energy (MGE)	Sep. 30, 2014 Alagasco	Sep. 30, 2015 Scenario, Forecast Office Building Laclede Gas	Sep. 30, 2015 Scenario, Forecast Additional Office Space Laclede Gas	Sep. 30, 2014 Vehicles and Power Operated Equipment Leases Laclede Gas
Loss Contingencies [Line Items]
Office headquarters lease rental aggregate expense		$ 1.0	$ 1.0	$ 0.9	$ 0.6	$ 1.8
Term of operating lease contract							20 years	10 years
Annual minimum rental payments		2.8
Minimum rental costs obligations - current fiscal year									2.7
Minimum rental costs obligations - due in two years									2.7
Minimum rental costs obligations - due in three years									0.1
Outstanding mortgage loans incurred in connection with various real estate ventures with general partners	$ 1.5