ACQUISITIONS AND DISPOSITIONS - Schedule of Net Assets Held for Sale (Details) - St. Lawrence Gas - Disposal group, held-for-sale, not discontinued operations - CAD CAD in Millions	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accounts receivable and other (current assets held for sale)	CAD 424	CAD 0
Deferred amounts and other assets (long-term assets held for sale)	1,190	278
Accounts payable and other (current liabilities held for sale)	(315)	0
Net assets held for sale	CAD 1,299	CAD 278