REGULATORY MATTERS (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended				0 Months Ended	12 Months Ended	0 Months Ended		12 Months Ended	0 Months Ended									0 Months Ended		12 Months Ended	165 Months Ended	12 Months Ended	0 Months Ended				15 Months Ended		0 Months Ended	15 Months Ended	0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Laclede Gas	Sep. 30, 2013 Laclede Gas	Jan. 01, 2014 APSC Alagasco	Sep. 30, 2014 APSC Alagasco	Apr. 12, 2014 ISRS charges from February 2013 - December 2013 MoPSC Laclede Gas	Jul. 25, 2014 ISRS charges from March 2014 - August 2014 MoPSC Laclede Gas	Sep. 30, 2014 ISRS charges MoPSC Laclede Gas	May 01, 2014 General Rate Case MoPSC Missouri Gas Energy (MGE)	Sep. 16, 2013 General Rate Case MoPSC Missouri Gas Energy (MGE)	Mar. 21, 2014 ISRS charges from January 2013 - September 2013 MoPSC Missouri Gas Energy (MGE)	Dec. 06, 2013 ISRS charges from January 2013 - September 2013 MoPSC Missouri Gas Energy (MGE)	Jul. 25, 2014 ISRS charges from January 2014 - August 2014 MoPSC Missouri Gas Energy (MGE)	Sep. 30, 2014 Enhanced stability reserve	Sep. 30, 2013 Enhanced stability reserve	Sep. 30, 2014 Enhanced stability reserve Laclede Gas	Sep. 30, 2013 Enhanced stability reserve Laclede Gas	Dec. 01, 2010 Enhanced stability reserve APSC Alagasco	Sep. 30, 2014 Enhanced stability reserve APSC Alagasco	Sep. 30, 2013 Deferred Costs Incurred Prior to YE 1999	Sep. 30, 2013 Deferred Costs Incurred Prior to YE 1999	Sep. 30, 2013 ISRS charges Missouri Gas Energy (MGE)	Oct. 01, 2014 Subsequent Event Missouri Gas Energy (MGE)	Oct. 18, 2014 Subsequent Event ISRS charges from March 2014 - August 2014 MoPSC Laclede Gas	Oct. 18, 2014 Subsequent Event ISRS charges from January 2014 - August 2014 MoPSC Missouri Gas Energy (MGE)	Jan. 01, 2014 Minimum APSC Alagasco	Dec. 31, 2013 Minimum APSC Alagasco	Sep. 30, 2014 Minimum Enhanced stability reserve APSC Alagasco	Jan. 01, 2014 Maximum APSC Alagasco	Dec. 31, 2013 Maximum APSC Alagasco	Dec. 01, 2014 Scenario, Forecast APSC Alagasco	Dec. 01, 2019 Scenario, Forecast Enhanced stability reserve APSC Alagasco
Public Utilities, General Disclosures [Line Items]
Regulatory assets for which no return on investment during recovery period is provided	$ 445.1	$ 388.4	$ 373.9	$ 388.4
Remaining recovery period for regulatory assets for which no return on investment during recovery period is provided	15 years
Requested rate increase								3.1			23.4		1.6	2.8
Regulatory assets	637.4	545.9	541.7	545.9											3.3	0	0	0			10.5	10.5
Regulatory assets amortization period																					15 years
Amortization of deferred costs recognized to date																						10.4
Approved rate increase							7.0		9.8	7.8		1.7													2.8	2.0						2.4
Amount of capitalized costs recovered																							6.3
Percent of distribution costs to be recovered																								83.00%
Approved return rate on equity (percent)					10.80%																						10.50%	13.15%		10.95%	13.65%
Maximum return on equity, percentage of prior year revenues (percent)						4.00%
Rate increase (decrease), margin of index range (percent)						1.75%
Self insurance policy limit per occurrence																				1
Extraordinary costs related to a single force majeure event limit																													0.3
Extraordinary costs related to multiple force majeure events limit																													0.4
Negative individual large commercial and industrial customer budget revenue variance minimum amount																													0.4
Revenue subject to refund recognition period																			9 years
Revenue subject to refund amortization period																																	5 years
Revenue subject to refund annual amortization limit																																	$ 0.7