AQUISITIONS AND DISPOSITIONS - Assets Held for Sale (Details) - Held-for-sale - CAD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts receivable and other (current assets held for sale)	$ 17	$ 28
Deferred amounts and other assets (long-term assets held for sale)	330	269
Accounts payable and other (current liabilities held for sale)	(8)	0
Net assets held for sale	339	297
Property, plant and equipment, noncurrent	$ 241	$ 181