Income Taxes - Deferred Income Tax Assets and Liabilities (Details) - CAD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax assets
Amount related to tax losses carried forward	$ 6	$ 11
Liabilities carrying value in excess of tax basis	139	97
Unrealized foreign exchange losses	26	85
Environmental remediation costs	22	23
Other	4	2
Total deferred income tax assets	197	218
Less: Valuation allowance	0	(5)
Total net deferred income tax assets	197	213
Deferred income tax liabilities
Properties carrying value in excess of tax basis	3,524	3,496
Pensions carrying value in excess of tax basis	83	164
Other	91	71
Total deferred income tax liabilities	3,698	3,731
Total net deferred income tax liabilities	$ 3,501	$ 3,518