CHANGES IN ACCOUNTING POLICIES (Details) - CAD ($) $ in Millions	Jan. 01, 2019	Sep. 30, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease right-of-use assets, net	$ 771	$ 733
Operating lease liability	856	$ 804
Lease impairment	$ 85
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	$ 771
Weighted average discount rate, percent	4.32%