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Stock-Based Compensation Plans - Stock Options (Narrative) (Details) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Stock options outstanding (shares) | 1.5 | 1.9
Stock options weighted average exercise price (CAD per share) | $ 48.96 | $ 48.12
Options vested, number of options (shares) | 1.4 | 1.6
Options vested, weighted average exercise price (CAD per share) | $ 48.87 | $ 47.19
Options exercised (shares) | 0.4 | 0.3
Proceeds from stock options exercised | $ 15 | $ 13
Stock options, intrinsic value | $ 5 | $ 6
Options |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Exercisable period | 10 years |
Expiration period after death or retirement | 3 years |
Award vesting period | 4 years |

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