SIGNIFICANT ACCOUNTING POLICIES - Useful Lives of Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2018
Pipeline facilities and compression equipment | Minimum
Property, Plant and Equipment
Estimated useful lives	20 years
Pipeline facilities and compression equipment | Maximum
Property, Plant and Equipment
Estimated useful lives	77 years
Metering and other | Minimum
Property, Plant and Equipment
Estimated useful lives	5 years
Metering and other | Maximum
Property, Plant and Equipment
Estimated useful lives	77 years