PROPERTY, PLANT AND EQUIPMENT - Narrative (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 3,000	$ 2,900	$ 2,900
Impairment loss	423	$ 1,104	$ 4,463
Access Northeast Project
Property, Plant and Equipment [Line Items]
Impairment loss	$ 105