CHANGES IN ACCOUNTING POLICIES (Details) - CAD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Additional deficit recorded in connection with the adoption of ASU 2016-13	$ (64,363)	$ (69,407)	$ (73,435)
Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Additional deficit recorded in connection with the adoption of ASU 2016-13	$ 9,995	6,314	$ 5,538	$ 2,468
Modified retrospective adoption of ASC | Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Additional deficit recorded in connection with the adoption of ASU 2016-13		$ 66		$ 86