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Regulatory Matters - Regulatory Assets and Liabilities - Footnote (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Aug. 01, 2023
USD ($)
Sep. 30, 2023
USD ($)
Dec. 31, 2024
USD ($)
Jan. 30, 2024
USD ($)
Dec. 31, 2023
USD ($)
Dec. 31, 2022
USD ($)
Mar. 01, 2020
MWac
Regulatory Liabilities [Line Items]              
Capital expenditure shortfall refundable to customers (percent)     80.00%        
Retroactive rate adjustment collection period     24 months        
Regulatory asset, amortization period     26 years        
Regulatory assets     $ 1,321,059   $ 1,327,683    
Mountain View Fire              
Regulatory Liabilities [Line Items]              
Accrued estimated losses     172,300        
Expected recoveries of insurance amount     116,000        
Expenses of wildlife memerandum account     56,300        
Insurance settlements receivable     $ 136,500        
Empire Electric System - Missouri              
Regulatory Liabilities [Line Items]              
Securitization of qualified extraordinary costs affirmed $ 290,383            
Deferred capitalized costs              
Regulatory Liabilities [Line Items]              
Regulatory asset, amortization period     20 years        
Capitalized operating and maintenance costs, recovery rate, (percent)     2.43%        
Regulatory assets     $ 178,412   124,517    
Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Asset retirement obligation           $ 21,283  
Regulatory assets     108,531   326,418    
Pension and post-employment benefits              
Regulatory Liabilities [Line Items]              
Regulatory assets     $ 51,819   68,822    
Future service years of employees     10 years        
Environmental costs              
Regulatory Liabilities [Line Items]              
Regulatory assets     $ 62,340   66,779    
Environmental remediation, rate recovery period     7 years        
Clean energy and other customer programs              
Regulatory Liabilities [Line Items]              
Regulatory assets     $ 40,492   37,214    
Retired generating plant              
Regulatory Liabilities [Line Items]              
Regulatory assets     $ 14,586   183,732    
Coal generation capacity (MW) | MWac             200
Long-term maintenance contract              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period     5 years        
Regulatory assets     $ 2,963   $ 4,932    
Minimum | Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Regulatory asset, amortization period     6 months        
Minimum | Pension and post-employment benefits              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period     3 years        
Minimum | Clean energy and other customer programs              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period     1 year        
Minimum | Rate review costs              
Regulatory Liabilities [Line Items]              
Costs capitalized and amortized period     1 year        
Maximum | Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Regulatory asset, amortization period     24 months        
Maximum | Pension and post-employment benefits              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period     8 years        
Maximum | Clean energy and other customer programs              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period     10 years        
Maximum | Rate review costs              
Regulatory Liabilities [Line Items]              
Costs capitalized and amortized period     5 years        
Rate adjustment mechanism | Minimum              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period     1 year        
Rate adjustment mechanism | Maximum              
Regulatory Liabilities [Line Items]              
Regulatory assets, recovery period     5 years        
Midwest Extreme Weather Event | Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Issuance of securitized tariff bonds, authorized amount           221,646  
Public utilities, incurred cost one-time net gain (loss) $ 63,495            
Public utilities, incurred cost one-time net gain (loss), net of tax   $ 48,452          
Midwest Extreme Weather Event | Empire Electric              
Regulatory Liabilities [Line Items]              
Issuance of securitized bonds for qualified extraordinary costs       $ 301,463      
Amortization expense     $ 15,939        
Energy Transistion Costs | Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Issuance of securitized tariff bonds, authorized amount           $ 140,774  
Securitized Utility Tariff Bonds due January 1, 2035 | Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Issuance of securitized tariff bonds, authorized amount       $ 180,500      
Percentage of public utilities, issuance of securitized tariff bonds       0.04943      
Securitized Utility Tariff Bonds due January 1, 2039 | Fuel and commodity cost adjustments              
Regulatory Liabilities [Line Items]              
Issuance of securitized tariff bonds, authorized amount       $ 125,000      
Percentage of public utilities, issuance of securitized tariff bonds       0.05091