PARTNERS' CAPITAL AND MEMBERSHIP INTERESTS (Mountaineer Acquisition) (Details) (Mountaineer Midstream, USD $)
0 Months Ended 12 Months Ended
Jun. 21, 2013
Jun. 03, 2013
Dec. 31, 2013
Business Acquisition [Line Items]      
Cost of acquired entity, purchase price $ 210,000,000    
Cost of acquired entity, cash paid 110,000,000    
Units issued to acquire entity 100,000,000   100,000,000
Volume weighted average share price, term   5 days  
Volume weighted average share price   $ 31.53  
Units issued in connection with acquisition     3,171,120.00
Cost of acquired entity, equity interests issued and issuable 100,000,000    
Limited partners, Common
     
Business Acquisition [Line Items]      
Units issued to acquire entity 98,000,000   98,000,000
Units issued in connection with acquisition 3,107,698   3,107,698
General Partner Units
     
Business Acquisition [Line Items]      
Units issued to acquire entity $ 2,000,000    
Units issued in connection with acquisition 63,422   63,422