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Commitments and Contingencies (Details)
$ in Millions
9 Months Ended 148 Months Ended
Jan. 01, 2024
USD ($)
trust
Jan. 17, 2023
USD ($)
Sep. 30, 2022
USD ($)
Jul. 03, 2018
Aug. 18, 2014
USD ($)
Sep. 30, 2024
USD ($)
timePeriod
trust
MW
Oct. 31, 2023
claim
Apr. 18, 2023
USD ($)
Schedule of Commitments and Contingencies [Line Items]                
Production tax credit guarantees           $ 29.0    
Kūpono Solar                
Schedule of Commitments and Contingencies [Line Items]                
Non recourse construction financing agreement               $ 140.0
Kūpono Solar                
Schedule of Commitments and Contingencies [Line Items]                
Project plant capacity (in MW's) | MW           42    
Asset purchase agreement           20 years    
APS                
Schedule of Commitments and Contingencies [Line Items]                
Maximum insurance against public liability per occurrence for a nuclear incident (up to) $ 16,300.0              
Maximum available nuclear liability insurance (up to) 500.0              
Remaining nuclear liability insurance through mandatory industry wide retrospective assessment program 15,800.0              
Maximum retrospective premium assessment per reactor for each nuclear liability incident 165.9              
Annual limit per incident with respect to maximum retrospective premium assessment $ 24.7              
Number of VIE lessor trusts | trust 3         3    
Maximum potential retrospective assessment per incident of APS $ 144.9              
Annual payment limitation with respect to maximum potential retrospective premium assessment $ 21.6              
Amount of "all risk" (including nuclear hazards) insurance for property damage to, and decontamination of, property at Palo Verde           $ 2,800.0    
Maximum amount that could be incurred under retrospective assessment of NEIL policies           23.1    
Collateral assurance provided based on rating triggers           $ 64.1    
Period to provide collateral assurance based on rating triggers           20 days    
Increase in contractual obligations           $ 5,500.0    
APS | Surety Bonds Expiring in 2025                
Schedule of Commitments and Contingencies [Line Items]                
Surety bonds expiring, amount           20.0    
APS | Letter of Credit                
Schedule of Commitments and Contingencies [Line Items]                
Outstanding letters of credit           19.0    
APS | Contaminated groundwater wells                
Schedule of Commitments and Contingencies [Line Items]                
Costs related to investigation and study under Superfund site           3.0    
Costs related to oversight and remedial investigation of superfund site   $ 1.7            
APS | Contaminated groundwater wells | Pending Litigation                
Schedule of Commitments and Contingencies [Line Items]                
Settlement amount     $ 8.3          
NTEC | Four Corners                
Schedule of Commitments and Contingencies [Line Items]                
Asset purchase agreement, option to purchase, ownership interest, percentage       7.00%        
Breach of Contract for Disposal of Spent Nuclear Fuel and/or High Level Radioactive Waste                
Schedule of Commitments and Contingencies [Line Items]                
Amount awarded from other party         $ 18.1 $ 156.6    
Breach of Contract for Disposal of Spent Nuclear Fuel and/or High Level Radioactive Waste | APS                
Schedule of Commitments and Contingencies [Line Items]                
Number of claims submitted | claim             10  
Gain contingency, number of settlement agreement time periods | timePeriod           10    
Amount awarded from other party         $ 5.3 $ 45.6