Leases - Supplemental Balance Sheet Information (Details) - CAD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Operating lease, ROU asset	$ 364	$ 347
Operating lease, ROU asset, location	Other assets (Note 19)	Other assets (Note 19)
Finance lease, ROU asset	$ 102	$ 111
Finance lease, ROU asset, location	Property balance	Property balance
Operating lease liabilities, current	$ 112	$ 102
Operating lease liabilities, current, location	Accounts payable and accrued liabilities (Note 15, 19)	Accounts payable and accrued liabilities (Note 15, 19)
Finance lease liabilities, current	$ 14	$ 14
Finance lease liabilities, current, location	Long-term debt maturing within one year (Note 16, 17, 19)	Long-term debt maturing within one year (Note 16, 17, 19)
Operating lease liabilities, long-term	$ 254	$ 242
Operating lease liabilities, long-term, location	Other long-term liabilities (Note 18, 19)	Other long-term liabilities (Note 18, 19)
Obligations under finance leases	$ 21	$ 31
Finance lease liabilities, long-term, location	Long-term debt	Long-term debt