Income Taxes - Deferred Income Tax Assets and Liabilities (Details) - CAD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax assets
Amount related to tax losses carried forward	$ 17	$ 6
Liabilities carrying value in excess of tax basis	131	139
Unrealized foreign exchange losses	4	26
Environmental remediation costs	22	22
Other	4	4
Total net deferred income tax assets	178	197
Deferred income tax liabilities
Properties carrying value in excess of tax basis	3,708	3,524
Pensions carrying value in excess of tax basis	43	83
Other	93	91
Total deferred income tax liabilities	3,844	3,698
Total net deferred income tax liabilities	$ 3,666	$ 3,501