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Employee Future Benefits - Fair Value of Plan Assets by Major Category (Details) - CAD ($) $ in Millions | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Disclosure of fair value of plan assets [line items] |  |
Alternative funds | $ 39 |
Money market and cash and cash equivalents | 20 | $ 20
Total | 289 | 353
Canadian |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 18 | 33
US |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 17 | 20
International |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 79 | 126
Private |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 1 | 1
AAA |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 24 | 28
AA |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 38 | 54
A |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 26 | 36
Loans | 1 |
BBB |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 19 | 25
Loans | 1 |
Below BBB |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 6 | 10
Level I |  |
Disclosure of fair value of plan assets [line items] |  |
Alternative funds | 0 |
Money market and cash and cash equivalents | 0 | 0
Total | 51 | 48
Level I | Canadian |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 0 | 0
Level I | US |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 12 | 0
Level I | International |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 38 | 47
Level I | Private |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 0 | 0
Level I | AAA |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 0 | 0
Level I | AA |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 0 | 0
Level I | A |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 0 | 0
Loans | 0 |
Level I | BBB |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 1 | 1
Loans | 0 |
Level I | Below BBB |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 0 | 0
Level II |  |
Disclosure of fair value of plan assets [line items] |  |
Alternative funds | 0 |
Money market and cash and cash equivalents | 20 | 20
Total | 198 | 300
Level II | Canadian |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 18 | 29
Level II | US |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 5 | 20
Level II | International |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 41 | 79
Level II | Private |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 0 | 0
Level II | AAA |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 24 | 28
Level II | AA |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 38 | 54
Level II | A |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 26 | 36
Loans | 1 |
Level II | BBB |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 18 | 24
Loans | 1 |
Level II | Below BBB |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 6 | 10
Level III |  |
Disclosure of fair value of plan assets [line items] |  |
Alternative funds | 39 |
Money market and cash and cash equivalents | 0 | 0
Total | 40 | 5
Level III | Canadian |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 0 | 4
Level III | US |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 0 | 0
Level III | International |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 0 | 0
Level III | Private |  |
Disclosure of fair value of plan assets [line items] |  |
Equity securities | 1 | 1
Level III | AAA |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 0 | 0
Level III | AA |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 0 | 0
Level III | A |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 0 | 0
Loans | 0 |
Level III | BBB |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | 0 | 0
Loans | 0 |
Level III | Below BBB |  |
Disclosure of fair value of plan assets [line items] |  |
Bonds | $ 0 | $ 0

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