SEGMENTED INFORMATION - GEOGRAPHIC INFORMATION (Details) - CAD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Geographic Information
Total operating revenues	$ 12,352	$ 11,598	$ 13,263	$ 12,856	$ 11,562	$ 11,345	$ 10,745	$ 12,726	$ 50,069	$ 46,378	$ 44,378
Property, plant and equipment, net	93,723				94,540				93,723	94,540
Canada
Geographic Information
Total operating revenues									19,954	19,023	18,076
Property, plant and equipment, net	45,993				44,716				45,993	44,716
United States
Geographic Information
Total operating revenues									30,115	27,355	$ 26,302
Property, plant and equipment, net	$ 47,730				$ 49,824				$ 47,730	$ 49,824