LEASES - LEASE COMMITMENTS (Details) - CAD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating leases
2021	$ 121
2022	116
2023	96
2024	90
2025	84
Thereafter	531
Total undiscounted lease payments	1,038
Less imputed interest	(277)
Total	761	$ 783
Finance leases
2021	18
2022	16
2023	16
2024	13
2025	6
Thereafter	84
Total undiscounted lease payments	153
Less imputed interest	(38)
Total	$ 115	$ 94