SIGNIFICANT ACCOUNTING POLICIES - Useful Lives of Plant, Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
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