Pensions and Other Benefits - Net Periodic Benefit Cost for DB Pension Plans and Other Benefits (Details) - CAD CAD in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pensions [Member]
Defined Benefit Plan Disclosure [Line Items]
Current service cost (benefits earned by employees in the period)	CAD 27	CAD 32
Interest cost on benefit obligation	117	115
Expected return on fund assets	(212)	(201)
Recognized net actuarial loss	48	66
Amortization of prior service costs	(2)	(1)
Net periodic benefit (recovery) cost	(22)	11
Other benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Current service cost (benefits earned by employees in the period)	3	3
Interest cost on benefit obligation	5	5
Expected return on fund assets	0	0
Recognized net actuarial loss	1	1
Amortization of prior service costs	0	0
Net periodic benefit (recovery) cost	CAD 9	CAD 9