Components of Net Periodic Benefit Cost (Detail) - CAD CAD in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
|
| Pension benefits | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Current service cost | CAD 50 | CAD 56 | CAD 152 | CAD 158 |
| Interest cost | 82 | 77 | 240 | 231 |
| Expected return on plan assets | (101) | (101) | (300) | (294) |
| Amortization of prior service cost | 2 | 4 | 7 | 12 |
| Amortization of actuarial loss | 39 | 50 | 121 | 149 |
| Net benefit cost | 72 | 86 | 220 | 256 |
| Other post-retirement benefits | ||||
| Defined Benefit Plan Disclosure [Line Items] | ||||
| Current service cost | 4 | 4 | 12 | 12 |
| Interest cost | 7 | 7 | 20 | 19 |
| Amortization of actuarial loss | 3 | 3 | 10 | 9 |
| Net benefit cost | CAD 14 | CAD 14 | CAD 42 | CAD 40 |