Income taxes - Deferred Income Tax Assets and Liabilities (Details) - CAD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Deferred income tax assets
Tax losses and other attributes carried forward	$ 298	$ 173
Liabilities carrying value in excess of tax basis	300	276
Unrealized foreign exchange losses	57	18
Environmental remediation costs	50	50
Other	10	7
Total deferred income tax assets	715	524
Valuation allowance	(57)	(36)
Total net deferred income tax assets	658	488
Deferred income tax liabilities
Properties carrying value in excess of tax basis	10,155	9,481
Pensions carrying value in excess of tax basis	1,084	751
Intangibles carrying value in excess of tax basis	824	789
Investments carrying value in excess of tax basis	498	473
Other	71	46
Total deferred income tax liabilities	12,632	11,540
Total net deferred income tax liabilities	$ 11,974	$ 11,052