Pensions and Other Benefits - Amounts Recognized in Company's Consolidated Balance Sheets (Detail) - CAD CAD in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Pension asset	CAD 1,401	CAD 304
Pension and other benefit liabilities	(758)	(755)
Pension Plans, Defined Benefit [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Pension asset	1,401	304
Accounts payable and accrued liabilities	(10)	(9)
Pension and other benefit liabilities	(285)	(279)
Total amount recognized	1,106	16
Other Postretirement Benefit Plans, Defined Benefit [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Pension asset	0	0
Accounts payable and accrued liabilities	(34)	(34)
Pension and other benefit liabilities	(473)	(476)
Total amount recognized	CAD (507)	CAD (510)