CHANGES IN ACCOUNTING POLICIES (Details) - CAD ($) $ in Millions	Jan. 01, 2019	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 771	$ 713
Operating lease liabilities	856	$ 783
Pre-existing liabilities related to impaired lease	$ 85
Weighted average discount rate (percent)	4.32%	4.30%
ASU 2016-02 (Topic 842)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets	$ 771
Operating lease liabilities	$ 771