Components of Net Periodic Benefit Cost (Detail) - CAD CAD in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Current service cost	CAD 51	CAD 39	CAD 102	CAD 77
Interest cost	77	80	154	159
Expected return on plan assets	(96)	(91)	(193)	(182)
Amortization of prior service cost	4	5	8	11
Amortization of actuarial loss	49	43	99	86
Net benefit cost	85	76	170	151
Other post-retirement benefits
Defined Benefit Plan Disclosure [Line Items]
Current service cost	4	2	8	5
Interest cost	6	6	12	12
Amortization of actuarial loss	3	2	6	4
Net benefit cost	CAD 13	CAD 10	CAD 26	CAD 21