Financial instruments (Details) - CAD ($) $ in Millions		12 Months Ended
	Jan. 12, 2024	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Investments [Line Items]
Long-term debt, excluding commercial paper		$ 20,749	$ 21,437
Long-term debt, fair value		18,911	20,550
Settlement of foreign currency forward contracts		65	0	$ 0
Treasury Rate Locks | Net Interest Expense
Schedule of Investments [Line Items]
Derivative losses amortized to net interest expense		6	7	6
Foreign Exchange Contract
Schedule of Investments [Line Items]
Foreign exchange loss on FX forward contracts		4	39
Settlement of foreign currency forward contracts	$ 65
Foreign currency contracts, liability, fair value			60
Net Investment Hedge
Schedule of Investments [Line Items]
Gain (loss) on derivative		$ (380)	$ 194	$ (471)