Financing Costs and Additional Notes and Loans Payable Information (Detail) - CAD CAD in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt-related interest		CAD 103	CAD 121	CAD 102
Capitalized interest		(38)	(49)	(68)
Net interest expense		65	72	34
Other interest		13	(7)	5
Total financing costs	[1]	CAD 78	CAD 65	CAD 39

[1] Cash interest payments in 2017 were $58 million (2016 - $73 million, 2015 - $74 million). The weighted average interest rate on short-term borrowings in 2017 was 0.9 percent (2016 - 0.8 percent, 2015 - 0.8 percent). Average effective rate on the long-term borrowings with ExxonMobil in 2017 was 1.3 percent (2016 - 1.0 percent, 2015 - 1.0 percent).