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Employee Future Benefits - Fair Value of Plan Assets by Major Category (Details) $ in Millions, $ in Millions | Dec. 31, 2024 CAD ($) | Jun. 30, 2024 CAD ($) | Jun. 30, 2024 USD ($) | Dec. 31, 2023 CAD ($)
--- | --- | --- | --- | ---
Disclosure of fair value of plan assets [line items] |  |  |  |
Loans | $ 1 |  |  | $ 2
Alternative funds | 46 |  |  | 44
Money market and cash and cash equivalents | 23 |  |  | 21
Total | 257 | $ 23 | $ 17 | 284
Canadian |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 12 |  |  | 12
US |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities |  |  |  | 6
International |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 53 |  |  | 86
Private |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 1 |  |  | 1
A - AAA |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 99 |  |  | 92
BBB |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 17 |  |  | 16
Below BBB |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 5 |  |  | 4
A |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Loans | 1 |  |  | 1
Level I |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Loans | 0 |  |  | 0
Alternative funds | 0 |  |  | 0
Money market and cash and cash equivalents | 2 |  |  | 2
Total | 2 |  |  | 3
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 |  |  |  | 0
Level I | International |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 0 |  |  | 0
Level I | Private |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 0 |  |  | 0
Level I | A - AAA |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 0 |  |  | 0
Level I | BBB |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 0 |  |  | 1
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] |  |  |  |
Loans | 1 |  |  | 2
Alternative funds | 0 |  |  | 0
Money market and cash and cash equivalents | 19 |  |  | 19
Total | 104 |  |  | 160
Level II | Canadian |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 12 |  |  | 12
Level II | US |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities |  |  |  | 6
Level II | International |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 53 |  |  | 86
Level II | Private |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 0 |  |  | 0
Level II | A - AAA |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 18 |  |  | 30
Level II | BBB |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 1 |  |  | 5
Level II | Below BBB |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 0 |  |  | 0
Level III |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Loans | 0 |  |  | 0
Alternative funds | 46 |  |  | 44
Money market and cash and cash equivalents | 2 |  |  | 0
Total | 151 |  |  | 121
Level III | Canadian |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities | 0 |  |  | 0
Level III | US |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Equity securities |  |  |  | 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 | A - AAA |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 81 |  |  | 62
Level III | BBB |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | 16 |  |  | 10
Level III | Below BBB |  |  |  |
Disclosure of fair value of plan assets [line items] |  |  |  |
Bonds | $ 5 |  |  | $ 4

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