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SIGNIFICANT ACCOUNTING POLICIES - Useful Lives of Plant, Property and Equipment (Details)
 12 Months Ended
Dec. 31, 2016
Pipeline facilities and compression equipment | Minimum  
PLANT, PROPERTY AND EQUIPMENT  
Estimated useful lives 20 years
Pipeline facilities and compression equipment | Maximum  
PLANT, PROPERTY AND EQUIPMENT  
Estimated useful lives 77 years
Metering and other equipment | Minimum  
PLANT, PROPERTY AND EQUIPMENT  
Estimated useful lives 5 years
Metering and other equipment | Maximum  
PLANT, PROPERTY AND EQUIPMENT  
Estimated useful lives 77 years