CHANGES IN ACCOUNTING POLICIES (Details) - CAD ($) $ in Millions	Jan. 01, 2019	Jun. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets, net	$ 771	$ 738
Lease impairment	85
Operating lease liability	$ 856	$ 813
Weighted average discount rate, percent	4.30%	4.30%
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets, net	$ 771
Operating lease liability	$ 856
Weighted average discount rate, percent	4.32%