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Regulation - Significant Regulatory Matters (Narrative) (Details) $ in Millions, $ in Millions |  | 1 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2024 | Nov. 30, 2024 | Oct. 31, 2024 | Aug. 31, 2024 | Jul. 31, 2024 | Dec. 31, 2024 CAD ($) | Dec. 31, 2023 CAD ($) | Dec. 31, 2024 USD ($)
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Regulatory liability |  |  |  |  |  | $ 4,291 | $ 3,958 |
FERC | ITC |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Allowed ROE | 10.02% |  | 9.98% |  |  | 10.73% | 10.77% |
Regulatory liability |  |  |  |  |  | $ 39 |  | $ 27
Refund with interest, period |  |  | 15 months |  |  |  |  |
FERC | ITC | Maximum |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Allowed ROE |  |  | 12.58% |  |  |  |  |
ACC | UNS Gas |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Allowed ROE |  |  |  |  |  | 9.75% | 9.75% |
ACC | UNS Gas | General rate application |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Requested return on equity |  | 10.25% |  |  |  |  |  |
Requested common equity |  | 56.00% |  |  |  |  |  |
PSC | Central Hudson |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Allowed ROE |  |  |  |  |  | 9.50% | 9.00% |
PSC | Central Hudson | General rate application |  |  |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |  |  |
Allowed ROE |  |  |  |  | 9.50% |  |  |
Requested return on equity |  |  |  | 10.00% |  |  |  |
Requested common equity |  |  |  | 48.00% |  |  |  |

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