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Regulatory Assets and Liabilities - Schedule of Regulatory Assets and Liabilities (Details) - CAD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
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