Pensions and Other Benefits - Summary of Defined Benefit Pension Plan Assets Measured at Fair Value Using Unobservable Inputs (Detail) - Real Estate [Member] - Pension Plans, Defined Benefit [Member] - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Beginning Balance	CAD 451	CAD 654
Disbursements	(36)	(223)
Net realized gains	24	64
Decrease in net unrealized gains	(2)	(44)
Ending Balance	CAD 437	CAD 451