CHANGES IN ACCOUNTING POLICIES (Details) - CAD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Deferred amounts and other assets	$ 5,614	$ 6,272	$ 6,442
Property, plant and equipment, net	92,521	90,823	90,711
Liabilities and equity
Accounts payable and other	6,823	9,540	9,478
Other long-term liabilities	8,390	7,576	7,510
Deferred income taxes	9,812	9,233	9,295
Redeemable noncontrolling interests	3,815	4,029	4,067
Retained deficit	$ (1,982)	(2,554)	(2,468)
Calculated under Revenue Guidance in Effect before Topic 606
Assets
Deferred amounts and other assets			6,442
Property, plant and equipment, net			90,711
Liabilities and equity
Accounts payable and other			9,478
Other long-term liabilities			7,510
Deferred income taxes			9,295
Redeemable noncontrolling interests			4,067
Retained deficit			$ (2,468)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Assets
Deferred amounts and other assets		(170)
Property, plant and equipment, net		112
Liabilities and equity
Accounts payable and other		62
Other long-term liabilities		66
Deferred income taxes		(62)
Redeemable noncontrolling interests		(38)
Retained deficit		$ (86)