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Regulatory Assets and Liabilities - Schedule of Regulatory Assets and Liabilities (Details) - CAD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
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Regulatory Assets [Line Items] |  |
Total regulatory assets | $ 4,631 | $ 4,384
Less: Current portion | (823) | (866)
Long-term regulatory assets | 3,808 | 3,518
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | 4,291 | 3,958
Less: Current portion | (595) | (577)
Long-term regulatory liabilities | 3,696 | 3,381
Future cost of removal (Note 3) |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | 1,728 | 1,547
Deferred income taxes (Note 3) |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | 1,329 | 1,280
Employee future benefits (Notes 3 and 24) |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | 459 | 294
Rate stabilization and related accounts |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | 208 | 292
Renewable energy surcharge |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | $ 155 | 129
Renewable energy surcharge | UNS Energy |  |
Regulatory Liabilities [Line Items] |  |
Renewable energy target (at least) (percent) | 15.00% |
Energy efficiency liability |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | $ 88 | 78
Electric and gas moderator account |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | 61 | 50
AESO Charges Deferral |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | 58 | 121
Other |  |
Regulatory Liabilities [Line Items] |  |
Total regulatory liabilities | 205 | 167
Other regulatory liabilities, individually less than threshold |  |
Regulatory Liabilities [Line Items] |  |
Threshold amount, other regulatory liabilities | 50 |
Deferred income taxes (Note 3) |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | 2,248 | 2,058
Deferred energy management costs |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | $ 591 | 521
Deferred energy management costs | Minimum |  |
Regulatory Assets [Line Items] |  |
Remaining recovery period | 1 year |
Deferred energy management costs | Maximum |  |
Regulatory Assets [Line Items] |  |
Remaining recovery period | 10 years |
Rate stabilization and related accounts |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | $ 453 | 521
Employee future benefits (Notes 3 and 24) |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | 235 | 254
Derivatives (Notes 3 and 26) | Energy contracts subject to regulatory deferral |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | 175 | 197
Deferred lease costs |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | 142 | 137
Deferred restoration costs |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | 133 | 115
Manufactured gas plant site remediation deferral (Note 16) |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | 82 | 81
Generation early retirement costs |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | 66 | 64
Renewable natural gas account |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | $ 58 | 47
Recovery period | 1 year |
Other |  |
Regulatory Assets [Line Items] |  |
Total regulatory assets | $ 448 | $ 389
Other regulatory assets, individually less than threshold |  |
Regulatory Assets [Line Items] |  |
Threshold amount, other regulatory assets | $ 50 |

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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 980 -SubTopic 340 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478742/980-340-50-1 + Details
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