COMMITMENTS AND CONTINGENCIES (Details) (USD $) In Millions, unless otherwise specified					9 Months Ended	12 Months Ended		9 Months Ended
	Sep. 30, 2014 site	Sep. 30, 2013 Removal Action, Phase I 35th Avenue Superfund Site Resident	Sep. 30, 2013 Removal Action, Phase II 35th Avenue Superfund Site Resident	Sep. 30, 2014 Sites owned by Alagasco site	Sep. 30, 2014 Natural Gas, Delivery and Storage	Dec. 31, 2013 Natural Gas, Delivery and Storage	Dec. 31, 2012 Natural Gas, Delivery and Storage	Sep. 30, 2014 Natural Gas MMcf
Site Contingency [Line Items]
Minimum total payments required for natural gas contracts					$ 134.0
Long-term contracts expense recognized in financial statements					$ 33.8	$ 50.0	$ 51.0
Long-term contracts, minimum quantity commitments (in millions of cubic feet)								111,000
Chain of title, manufactured gas plant sites	9			4
Chain of title, manufactured gas distribution sites	5			1
Site contingency, number of residents contaminated		50	30