Leases - Supplemental Balance Sheet Information (Details) - CAD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating lease, ROU asset	$ 347	$ 267
Operating lease, ROU asset, location	Other assets (Note 20)	Other assets (Note 20)
Finance lease, ROU asset	$ 111	$ 102
Finance lease, ROU asset, location	Properties	Properties
Operating lease liabilities, current	$ 102	$ 68
Operating lease liabilities, current, location	Accounts payable and accrued liabilities (Note 16, 20)	Accounts payable and accrued liabilities (Note 16, 20)
Finance lease liabilities, current	$ 14	$ 8
Finance lease liabilities, current, location	Long-term debt maturing within one year (Note 17, 18, 20)	Long-term debt maturing within one year (Note 17, 18, 20)
Operating lease liabilities, long-term	$ 242	$ 202
Operating lease liabilities, long-term, location	Other long-term liabilities (Note 19, 20)	Other long-term liabilities (Note 19, 20)
Finance lease liabilities, long-term	$ 31	$ 30
Finance lease liabilities, long-term, location	Long-term debt	Long-term debt