COMMITMENTS AND CONTINGENCIES - Contingencies (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	12 Months Ended	36 Months Ended						12 Months Ended
	Jul. 16, 2013 Laclede Gas	Sep. 30, 2014 Laclede Gas site	Sep. 30, 2007 Laclede Gas	Aug. 30, 2014 Laclede Gas	Sep. 30, 2014 Alagasco site	Sep. 30, 2013 Previous Ownership Laclede Gas site	Sep. 30, 2013 Previous Ownership Missouri Gas Energy (MGE) site	Sep. 30, 2014 Current Ownership Alagasco site	Sep. 30, 2014 Three-year period ending September 30, 2016 Laclede Gas	Sep. 30, 2014 From October 1, 2016 Laclede Gas	Dec. 31, 2013 Removal Action 35th Avenue Superfund Site Alagasco Resident
Site Contingency [Line Items]
Number of former manufactured gas plant (MGP) sites in Missouri		3
Number of former manufactured gas plant (MGP) sites in Shrewsbury, Missouri		1
Number of former manufactured gas plant (MGP) sites in the City of St. Louis		2
Number of former manufactured gas plant (MGP)					9	19	7	4
Minimum cost estimate for a one-time contractual transfer of risk				$ 8.1
Maximum cost estimate for a one-time contractual transfer of risk				39.3
Mopsc original proposed disallowance related to purchased gas costs			6.0
Revenue Sharing Agreements, Term	3 years
Revenue sharing agreements, Company's net margin amount subject to reduced sharing percentage		$ 2.0
Revenue sharing agreements, Company's net margin amount subject to reduced sharing percentage, Company's percentage share		15.00%							0.00%	15.00%
Number of former manufactured gas distribution					5			1
Number of residents at high levels of contamination											50