Financial instruments (Details) - CAD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jan. 12, 2024	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Schedule of Investments [Line Items]
Debt and finance lease liabilities, carrying value		$ 21,928		$ 21,928		$ 20,749
Debt and finance lease liabilities, fair value		20,508		20,508		18,911
Payments for settlement of foreign currency forward contracts		0	$ 0	0	$ 65
Foreign Exchange Contract
Schedule of Investments [Line Items]
Payments for settlement of foreign currency forward contracts	$ 65
Loss on derivative				0	4
Foreign currency contracts, fair value		0		0		$ 0
Net Investment Hedge
Schedule of Investments [Line Items]
Unrealized gain (loss) on net investment hedge		$ 299	$ (41)	$ 305	$ (144)