Leases Maturities of Lease Liabilities (Details) $ in Millions	Dec. 31, 2019 CAD ($)
Leases [Abstract]
Finance Leases, Payments due 2020	$ 11
Finance Leases, Payments due 2021	10
Finance Leases, Payments due 2022	108
Finance Leases, Payments due 2023	8
Finance Leases, Payments due 2024	9
Finance Leases, Payments due thereafter	21
Finance Leases, Total lease payments	167
Finance Leases, Imputed interest	(16)
Finance Leases, Present value of lease payments	151
Operating Leases, Payments due 2020	80
Operating Leases, Payments due 2021	55
Operating Leases, Payments due 2022	51
Operating Leases, Payments due 2023	39
Operating Leases, Payments due 2024	40
Operating Leases, Payments due thereafter	130
Operating Leases, Total lease payments	395
Operating Leases, Imputed interest	(41)
Operating Leases, Present value of lease payments	$ 354