Leased Facilities - Additional Information (Detail) CAD in Millions	Dec. 31, 2017 CAD
Operating Leased Assets [Line Items]
Minimum undiscounted lease commitments	CAD 199	[1]

[1] Net rental cost under cancelable and non-cancelable operating leases incurred in 2017 was $206 million (2016 - $253 million, 2015 - $311 million). Related rental income was not material.