ACQUISITIONS AND DISPOSITIONS - Schedule of Net Assets Held for Sale (Details) - Disposal group, held-for-sale, not discontinued operations - CAD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts receivable and other (current assets held for sale)	$ 28	$ 117
Deferred amounts and other assets (long-term assets held for sale)	269	2,383
Accounts payable and other (current liabilities held for sale)	0	(63)
Other long-term liabilities (long-term liabilities held for sale)	0	(96)
Net assets held for sale	297	2,341
Disposal group, property, plant and equipment, noncurrent	$ 181	$ 2,100