PROPERTY, PLANT AND EQUIPMENT - Schedule of Property, Plant and Equipment (Details) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
PROPERTY, PLANT AND EQUIPMENT
Total property, plant and equipment	CAD 105,813	CAD 78,895
Total accumulated depreciation	(15,102)	(14,611)
Property, plant and equipment, net	CAD 90,711	64,284
Pipeline
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	2.50%
Total property, plant and equipment	CAD 47,720	34,474
Pumping equipment, buildings, tanks and other
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	2.90%
Total property, plant and equipment	CAD 16,610	15,554
Land and right-of-way1
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	2.10%
Total property, plant and equipment	CAD 2,538	2,067
Gas mains, services and other
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	2.10%
Total property, plant and equipment	CAD 17,026	10,022
Compressors, meters and other operating equipment
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	2.10%
Total property, plant and equipment	CAD 5,774	4,014
Processing and treating plants
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	3.10%
Total property, plant and equipment	CAD 1,440	846
Storage
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	2.00%
Total property, plant and equipment	CAD 1,545	0
Wind turbines, solar panels and other
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	3.30%
Total property, plant and equipment	CAD 4,804	4,259
Power transmission
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	2.20%
Total property, plant and equipment	CAD 365	378
Vehicles, office furniture, equipment and other buildings and improvements
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	6.50%
Total property, plant and equipment	CAD 390	315
Under construction
PROPERTY, PLANT AND EQUIPMENT
Weighted Average Depreciation Rate	0.00%
Total property, plant and equipment	CAD 7,601	CAD 6,966