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Commitments and Contingencies (Collaborative Arrangements) (Narrative) (Details) - Jointly Owned Electricity Generation Plant - NSPI - CAD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items] |  |
Regulated fuel for generation and purchased power | $ 12 | $ 8
Operating, maintenance and general (OM&G) | $ 3 | $ 3

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