Income Taxes - Deferred Income Tax Assets and Liabilities (Details) - CAD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets
Amount related to tax losses carried forward	$ 11	$ 12
Liabilities carrying value in excess of tax basis	97	77
Unrealized foreign exchange losses	85	11
Environmental remediation costs	23	16
Other	2	11
Total deferred income tax assets	218	127
Valuation Allowance	(5)	0	$ 0
Total net deferred income tax assets	213	127
Deferred income tax liabilities
Properties carrying value in excess of tax basis	3,496	3,181
Pensions carrying value in excess of tax basis	164	226
Other	71	41
Total deferred income tax liabilities	3,731	3,448
Total net deferred income tax liabilities	$ 3,518	$ 3,321