Income Taxes - Deferred Income Tax Assets and Liabilities (Details) - CAD CAD in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred income tax assets
Amount related to tax losses carried forward	CAD 18	CAD 16
Liabilities carrying value in excess of tax basis	149	89
Future environmental remediation costs	30	33
Tax credits carried forward including minimum tax	0	0
Other	58	72
Total deferred income tax assets	255	210
Deferred income tax liabilities
Properties carrying value in excess of tax basis	3,796	3,553
Other	30	48
Total deferred income tax liabilities	3,826	3,601
Total net deferred income tax liabilities	CAD 3,571	CAD 3,391