Pensions and Other Benefits - Information About DB Pension Plans and Other Benefits (Detail) - CAD CAD in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of fund assets at January 1	CAD 11,376
Employer contributions	90	CAD 88	CAD 105
Fair value of fund assets at December 31	12,300	11,376
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	11,360	9,921
Current service cost	126	106	135
Interest cost	463	477	445
Employee contributions	43	51
Benefits paid	(608)	(579)
Foreign currency changes	42	15
Plan amendments and other	(6)	0
Actuarial loss (gain)	(226)	1,369
Projected benefit obligation at December 31	11,194	11,360	9,921
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of fund assets at January 1	11,376	10,722
Actual return on fund assets	1,374	1,088
Employer contributions	81	80
Employee contributions	43	51
Benefits paid	(608)	(579)
Foreign currency changes	34	14
Fair value of fund assets at December 31	12,300	11,376	10,722
Funded status - plan surplus (deficit)	1,106	16
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at January 1	517	483
Current service cost	12	14	16
Interest cost	21	23	21
Employee contributions	1	0
Benefits paid	(34)	(27)
Foreign currency changes	4	2
Plan amendments and other	0	0
Actuarial loss (gain)	(8)	22
Projected benefit obligation at December 31	513	517	483
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of fund assets at January 1	7	8
Actual return on fund assets	(1)	0
Employer contributions	33	26
Employee contributions	1	0
Benefits paid	(34)	(27)
Foreign currency changes	0	0
Fair value of fund assets at December 31	6	7	CAD 8
Funded status - plan surplus (deficit)	CAD (507)	CAD (510)