AQUISITIONS AND DISPOSITIONS - Assets Held for Sale (Details) - Disposal Group, Held-for-sale, Not Discontinued Operations - CAD ($) $ in Millions	Mar. 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)	$ 101	$ 117
Deferred amounts and other assets (long-term assets held for sale)	2,415	2,383
Accounts payable and other (current liabilities held for sale)	(55)	(63)
Other long-term liabilities (long-term liabilities held for sale)	(99)	(96)
Net assets held for sale	2,362	2,341
Property, plant and equipment, noncurrent	$ 2,200	$ 2,100