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Regulatory Assets and Liabilities - Schedule of Regulatory Assets and Liabilities (Details) - CAD ($)
$ in Millions
Dec. 31, 2023
Dec. 31, 2022
Regulatory Assets [Line Items]    
Total regulatory assets $ 4,384 $ 4,009
Less: Current portion (866) (914)
Long-term regulatory assets 3,518 3,095
Regulatory Liabilities [Line Items]    
Total regulatory liabilities 3,958 3,915
Less: Current portion (577) (595)
Long-term regulatory liabilities 3,381 3,320
Future cost of removal (Note 3)    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities 1,547 1,306
Deferred income taxes (Note 3)    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities 1,280 1,364
Employee future benefits (Notes 3 and 24)    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities 294 306
Rate stabilization and related accounts    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities 292 297
Renewable energy surcharge    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities $ 129 126
Renewable energy surcharge | UNS Energy    
Regulatory Liabilities [Line Items]    
Renewable energy target (at least) (percent) 15.00%  
AESO Charges Deferral    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities $ 121 21
Energy efficiency liability    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities 78 89
Derivatives (Notes 3 and 26) | Energy contracts subject to regulatory deferral    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities 37 224
Other    
Regulatory Liabilities [Line Items]    
Total regulatory liabilities 180 182
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 2,058 1,874
Rate stabilization and related accounts    
Regulatory Assets [Line Items]    
Total regulatory assets 521 557
Deferred energy management costs    
Regulatory Assets [Line Items]    
Total regulatory assets $ 521 445
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  
Employee future benefits (Notes 3 and 24)    
Regulatory Assets [Line Items]    
Total regulatory assets $ 254 207
Derivatives (Notes 3 and 26) | Energy contracts subject to regulatory deferral    
Regulatory Assets [Line Items]    
Total regulatory assets 197 84
Deferred lease costs    
Regulatory Assets [Line Items]    
Total regulatory assets 137 132
Deferred restoration costs    
Regulatory Assets [Line Items]    
Total regulatory assets 115 91
Manufactured gas plant site remediation deferral (Note 16)    
Regulatory Assets [Line Items]    
Total regulatory assets 81 97
Generation early retirement costs    
Regulatory Assets [Line Items]    
Total regulatory assets 64 78
Other    
Regulatory Assets [Line Items]    
Total regulatory assets 436 $ 444
Other regulatory assets, individually less than threshold    
Regulatory Assets [Line Items]    
Threshold amount, other regulatory assets $ 50