SEGMENTED INFORMATION - GEOGRAPHIC INFORMATION (Details) - CAD CAD in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Geographic Information
Revenues	CAD 12,889	CAD 9,227	CAD 11,116	CAD 11,146	CAD 9,338	CAD 8,488	CAD 7,939	CAD 8,795	CAD 44,378	CAD 34,560	CAD 33,794
Property, plant and equipment, net	90,711				64,284				90,711	64,284
Canada
Geographic Information
Revenues									18,076	12,470	11,087
Property, plant and equipment, net	46,025				32,008				46,025	32,008
United States
Geographic Information
Revenues									26,302	22,090	CAD 22,707
Property, plant and equipment, net	CAD 44,686				CAD 32,276				CAD 44,686	CAD 32,276