INTANGIBLE ASSETS (Details) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
INTANGIBLE ASSETS
Cost	CAD 4,138	CAD 2,387
Accumulated Amortization	871	814
Net	3,267	1,573
Amortization expenses
Amortization expense for intangible assets	280	CAD 177	CAD 158
Expected amortization expense for intangible assets
2018	264
2019	240
2020	217
2021	197
2022	CAD 179
Customer relationships
INTANGIBLE ASSETS
Weighted Average Amortization Rate (as a percent)	3.50%	3.00%
Cost	CAD 967	CAD 251
Accumulated Amortization	41	4
Net	CAD 926	CAD 247
Natural gas supply opportunities
INTANGIBLE ASSETS
Weighted Average Amortization Rate (as a percent)		3.20%
Cost		CAD 435
Accumulated Amortization		127
Net		CAD 308
Power purchase agreements
INTANGIBLE ASSETS
Weighted Average Amortization Rate (as a percent)	3.50%	3.20%
Cost	CAD 99	CAD 100
Accumulated Amortization	17	14
Net	CAD 82	CAD 86
Project agreement
INTANGIBLE ASSETS
Weighted Average Amortization Rate (as a percent)	4.00%
Cost	CAD 150
Accumulated Amortization	3
Net	CAD 147
Software
INTANGIBLE ASSETS
Weighted Average Amortization Rate (as a percent)	11.30%	11.80%
Cost	CAD 1,760	CAD 1,388
Accumulated Amortization	714	607
Net	CAD 1,046	CAD 781
Other intangible assets3
INTANGIBLE ASSETS
Weighted Average Amortization Rate (as a percent)	4.40%	4.80%
Cost	CAD 1,162	CAD 213
Accumulated Amortization	96	62
Net	CAD 1,066	CAD 151