Pensions and Other Benefits - Net Periodic Benefit Cost for DB Pension Plans and Other Benefits (Detail) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current service cost (benefits earned by employees in the year)	CAD 126	CAD 106	CAD 135
Interest cost on benefit obligation	463	477	445
Expected return on fund assets	(816)	(757)	(746)
Recognized net actuarial loss (gain)	265	190	267
Amortization of prior service costs	(6)	(68)	(58)
Net periodic benefit cost (recovery)	32	(52)	43
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current service cost (benefits earned by employees in the year)	12	14	16
Interest cost on benefit obligation	21	23	21
Expected return on fund assets	0	0	0
Recognized net actuarial loss (gain)	2	(2)	(11)
Amortization of prior service costs	1	0	0
Net periodic benefit cost (recovery)	CAD 36	CAD 35	CAD 26