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Fair Value of Pension Plan Assets Including Level Within Fair Value Hierarchy (Detail) - CAD ($) $ in Millions | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | $ 8,599 | $ 7,691
Investments that are measured at fair value using net asset value | 8,559 | 7,658
Canadian Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | 210 | 170
Investments that are measured at fair value using net asset value | 210 | 170
Non-Canadian Equity Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | 2,449 | 2,035
Investments that are measured at fair value using net asset value | 2,449 | 2,035
Corporate Debt Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | 1,379 | 1,231
Investments that are measured at fair value using net asset value | 1,379 | 1,231
Government Debt Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | 4,299 | 3,987
Investments that are measured at fair value using net asset value | 4,299 | 3,987
Asset Backed Debt Securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | 1 | 3
Investments that are measured at fair value using net asset value | 1 | 3
Equities - Venture Capital |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | 204 | 226
Investments that are measured at fair value using net asset value | 204 | 226
Cash |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | 57 | 39
Investments that are measured at fair value using net asset value | 17 | 6
Level 1 |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | 40 | 33
Level 1 | Cash |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Total plan assets at fair value | $ 40 | $ 33

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