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COMMITMENTS AND CONTINGENCIES - Contingencies (Details)
6 Months Ended 57 Months Ended
Dec. 17, 2013
fatality
Mar. 31, 2017
plaintiff
site
lawsuit
Dec. 31, 2016
lawsuit
Sep. 30, 2014
site
Laclede Gas        
Loss Contingencies [Line Items]        
Number of former manufactured gas plant (MGP) sites in Missouri   4    
Number of former manufactured gas plant (MGP) sites enrolled in BVCP   2    
Alagasco        
Loss Contingencies [Line Items]        
Number of former manufactured gas plant (MGP)   9    
Number of former manufactured gas distribution   5    
Number of incident fatalities | fatality 1      
Mobile Gas Service Corporation [Member]        
Loss Contingencies [Line Items]        
Number of lawsuits filed | lawsuit     14  
Number of lawsuits settled | lawsuit     11  
Number of lawsuits pending | lawsuit   3    
Previous Ownership | Laclede Gas        
Loss Contingencies [Line Items]        
Number of former manufactured gas plant (MGP)       19
Previous Ownership | Missouri Gas Energy (MGE)        
Loss Contingencies [Line Items]        
Number of former manufactured gas plant (MGP)   7    
Previous Ownership | Mobile Gas Service Corporation [Member]        
Loss Contingencies [Line Items]        
Number of former manufactured gas plant (MGP)   1    
Current Ownership | Alagasco        
Loss Contingencies [Line Items]        
Number of former manufactured gas plant (MGP)   4    
Number of former manufactured gas distribution   1    
Pending Litigation [Member] | Mobile Gas Service Corporation [Member]        
Loss Contingencies [Line Items]        
Number of plaintiffs | plaintiff   270    
Shrewsbury, Missouri | Laclede Gas        
Loss Contingencies [Line Items]        
Number of former manufactured gas plant (MGP) sites in Missouri   1    
St. Louis, Missouri | Laclede Gas        
Loss Contingencies [Line Items]        
Number of former manufactured gas plant (MGP) sites in Missouri   3