Pensions and Other Benefits - Amounts Recognized in Accumulated Other Comprehensive Losses (Detail) - CAD CAD in Millions	Dec. 31, 2015	Dec. 31, 2014
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Amounts for defined benefit pension and other post-retirement plans not recognized in income	CAD (1,504)	CAD (2,282)
Pension Plans, Defined Benefit [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Other than deferred investment gains	3,144	3,895
Deferred investment gains	(1,101)	(803)
Prior service cost	(20)	(20)
Deferred income tax	(580)	(858)
Amounts for defined benefit pension and other post-retirement plans not recognized in income	1,443	2,214
Other Postretirement Benefit Plans, Defined Benefit [Member]
Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items]
Other than deferred investment gains	77	86
Deferred investment gains	0	0
Prior service cost	4	5
Deferred income tax	(20)	(23)
Amounts for defined benefit pension and other post-retirement plans not recognized in income	CAD 61	CAD 68