LEASES - NARRATIVE (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 CAD ($)
Lessee, Lease, Description [Line Items]
Operating lease, expense	$ 113
Operating lease, payments	$ 123
Minimum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, remaining lease term	3 months
Lessor, operating lease, remaining lease term	2 months
Maximum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, remaining lease term	28 years
Lessor, operating lease, remaining lease term	24 years