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EFFECTS OF REGULATION - Regulatory Assets (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Nov. 30, 2025
Dec. 31, 2024
Feb. 20, 2021
Regulatory Asset [Line Items]        
Total Current Regulatory Assets $ 426   $ 446  
Total Noncurrent Regulatory Assets 4,804   5,129  
SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Current Regulatory Assets 115   107  
Total Noncurrent Regulatory Assets 903   921  
Unrecovered Winter Storm Fuel Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets       $ 106
Unrecovered Winter Storm Fuel Costs | SOUTHWESTERN ELECTRIC POWER COMPANY | Arkansas        
Regulatory Asset [Line Items]        
Remaining Recovery Period       6 years
Total Noncurrent Regulatory Assets       $ 22
Unrecovered Winter Storm Fuel Costs | SOUTHWESTERN ELECTRIC POWER COMPANY | Louisiana        
Regulatory Asset [Line Items]        
Remaining Recovery Period   5 years    
Total Noncurrent Regulatory Assets       $ 41
Unrecovered Winter Storm Fuel Costs | SOUTHWESTERN ELECTRIC POWER COMPANY | Texas        
Regulatory Asset [Line Items]        
Remaining Recovery Period       5 years
Total Noncurrent Regulatory Assets       $ 43
Pending final regulatory approval        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 1,307   1,311  
Pending final regulatory approval | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 445   454  
Approved for recovery        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 3,497   3,818  
Approved for recovery | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 458   467  
Earns/earning a return | Under-recovered Fuel Costs        
Regulatory Asset [Line Items]        
Total Current Regulatory Assets $ 140   246  
Remaining Recovery Period 1 year      
Earns/earning a return | Under-recovered Fuel Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Current Regulatory Assets $ 31   23  
Remaining Recovery Period 1 year      
Earns/earning a return | Unrecovered Winter Storm Fuel Costs        
Regulatory Asset [Line Items]        
Total Current Regulatory Assets $ 84   84  
Remaining Recovery Period 1 year      
Earns/earning a return | Unrecovered Winter Storm Fuel Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Current Regulatory Assets $ 84   84  
Remaining Recovery Period 1 year      
Earns/earning a return | Pending final regulatory approval        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets $ 435   395  
Earns/earning a return | Pending final regulatory approval | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 316   346  
Earns/earning a return | Pending final regulatory approval | Unrecovered Winter Storm Fuel Costs        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 0   33  
Earns/earning a return | Pending final regulatory approval | Unrecovered Winter Storm Fuel Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 0   33  
Earns/earning a return | Pending final regulatory approval | Welsh Plant, Units 1 and 3 Accelerated Depreciation        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 220   169  
Earns/earning a return | Pending final regulatory approval | Welsh Plant, Units 1 and 3 Accelerated Depreciation | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 220   169  
Earns/earning a return | Pending final regulatory approval | Pirkey Plant Accelerated Depreciation        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 93   121  
Earns/earning a return | Pending final regulatory approval | Pirkey Plant Accelerated Depreciation | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 93   121  
Earns/earning a return | Pending final regulatory approval | Unified Tracker Mechanism Deferred Costs        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 56   0  
Earns/earning a return | Pending final regulatory approval | Storm-Related Costs        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 43   51  
Earns/earning a return | Pending final regulatory approval | Storm-Related Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 2   10  
Earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 23   21  
Earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 1   1  
Earns/earning a return | Approved for recovery        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 1,341   1,711  
Earns/earning a return | Approved for recovery | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets $ 301   293  
Earns/earning a return | Approved for recovery | Unrecovered Winter Storm Fuel Costs        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 22   63  
Earns/earning a return | Approved for recovery | Unrecovered Winter Storm Fuel Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 22   63  
Earns/earning a return | Approved for recovery | Pirkey Plant Accelerated Depreciation | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Remaining Recovery Period 7 years      
Total Noncurrent Regulatory Assets $ 72   66  
Earns/earning a return | Approved for recovery | Storm-Related Costs        
Regulatory Asset [Line Items]        
Remaining Recovery Period 6 years      
Total Noncurrent Regulatory Assets $ 100   107  
Earns/earning a return | Approved for recovery | Storm-Related Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Remaining Recovery Period 3 years      
Total Noncurrent Regulatory Assets $ 10   0  
Earns/earning a return | Approved for recovery | Plant Retirement Costs - Asset Retirement Obligation Costs        
Regulatory Asset [Line Items]        
Remaining Recovery Period 15 years      
Total Noncurrent Regulatory Assets $ 1   111  
Earns/earning a return | Approved for recovery | Plant Retirement Costs - Unrecovered Plant        
Regulatory Asset [Line Items]        
Remaining Recovery Period 21 years      
Total Noncurrent Regulatory Assets $ 470   661  
Earns/earning a return | Approved for recovery | Long-term Under-recovered Fuel Costs - West Virginia        
Regulatory Asset [Line Items]        
Remaining Recovery Period 9 years      
Total Noncurrent Regulatory Assets $ 254   284  
Earns/earning a return | Approved for recovery | Pirkey Plant Accelerated Depreciation - Louisiana        
Regulatory Asset [Line Items]        
Remaining Recovery Period 7 years      
Total Noncurrent Regulatory Assets $ 72   66  
Earns/earning a return | Approved for recovery | Fuel Mine Closure Costs - Texas        
Regulatory Asset [Line Items]        
Remaining Recovery Period 10 years      
Total Noncurrent Regulatory Assets $ 65   71  
Earns/earning a return | Approved for recovery | Fuel Mine Closure Costs - Texas | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Remaining Recovery Period 10 years      
Total Noncurrent Regulatory Assets $ 65   71  
Earns/earning a return | Approved for recovery | Pirkey Plant Accelerated Depreciation - Arkansas        
Regulatory Asset [Line Items]        
Remaining Recovery Period 10 years      
Total Noncurrent Regulatory Assets $ 41   0  
Earns/earning a return | Approved for recovery | Pirkey Plant Accelerated Depreciation - Arkansas | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Remaining Recovery Period 10 years      
Total Noncurrent Regulatory Assets $ 41   0  
Earns/earning a return | Approved for recovery | PJM/SPP Annual Formula Rate True-up        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 35   0  
Earns/earning a return | Approved for recovery | Rockport Plant Dry Sorbent Injection System and Selective Catalytic Reduction        
Regulatory Asset [Line Items]        
Remaining Recovery Period 3 years      
Total Noncurrent Regulatory Assets $ 28   37  
Earns/earning a return | Approved for recovery | Texas Mobile Temporary Emergency Electric Energy Facilities Rider        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 27   33  
Earns/earning a return | Approved for recovery | Environmental Control Projects        
Regulatory Asset [Line Items]        
Remaining Recovery Period 15 years      
Total Noncurrent Regulatory Assets $ 27   29  
Earns/earning a return | Approved for recovery | Kentucky Deferred Purchased Power Expenses        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 0   45  
Earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 199   204  
Earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 18   12  
Does not earns/earning a return | Under-recovered Fuel Costs        
Regulatory Asset [Line Items]        
Total Current Regulatory Assets $ 202   116  
Remaining Recovery Period 1 year      
Does not earns/earning a return | Pending final regulatory approval        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets $ 872   916  
Does not earns/earning a return | Pending final regulatory approval | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 129   108  
Does not earns/earning a return | Pending final regulatory approval | Storm-Related Costs        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 191   301  
Does not earns/earning a return | Pending final regulatory approval | Storm-Related Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 43   40  
Does not earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 163   87  
Does not earns/earning a return | Pending final regulatory approval | Other Regulatory Assets Pending Final Regulatory Approval | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 20   18  
Does not earns/earning a return | Pending final regulatory approval | Plant Retirement Costs - Asset Retirement Obligation Costs        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 257   357  
Does not earns/earning a return | Pending final regulatory approval | Virginia Under Earnings        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 172   78  
Does not earns/earning a return | Pending final regulatory approval | NOLC Costs        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 89   93  
Does not earns/earning a return | Pending final regulatory approval | NOLC Costs | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 66   50  
Does not earns/earning a return | Approved for recovery        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 2,156   2,107  
Does not earns/earning a return | Approved for recovery | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets $ 157   174  
Does not earns/earning a return | Approved for recovery | Storm-Related Costs        
Regulatory Asset [Line Items]        
Remaining Recovery Period 6 years      
Total Noncurrent Regulatory Assets $ 158   67  
Does not earns/earning a return | Approved for recovery | Plant Retirement Costs - Asset Retirement Obligation Costs        
Regulatory Asset [Line Items]        
Remaining Recovery Period 17 years      
Total Noncurrent Regulatory Assets $ 459   360  
Does not earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets 222   229  
Does not earns/earning a return | Approved for recovery | Other Regulatory Assets Approved for Recovery | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets $ 25   23  
Does not earns/earning a return | Approved for recovery | Pension and OPEB Funded Status        
Regulatory Asset [Line Items]        
Remaining Recovery Period 12 years      
Total Noncurrent Regulatory Assets $ 796   974  
Does not earns/earning a return | Approved for recovery | Pension and OPEB Funded Status | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Remaining Recovery Period 12 years      
Total Noncurrent Regulatory Assets $ 77   93  
Does not earns/earning a return | Approved for recovery | Unamortized Loss on Reacquired Debt        
Regulatory Asset [Line Items]        
Remaining Recovery Period 23 years      
Total Noncurrent Regulatory Assets $ 85   91  
Does not earns/earning a return | Approved for recovery | Cook Plant Nuclear Refueling Outage Levelization        
Regulatory Asset [Line Items]        
Remaining Recovery Period 3 years      
Total Noncurrent Regulatory Assets $ 82   43  
Does not earns/earning a return | Approved for recovery | Unrealized Loss on Forward Commitments        
Regulatory Asset [Line Items]        
Remaining Recovery Period 7 years      
Total Noncurrent Regulatory Assets $ 69   53  
Does not earns/earning a return | Approved for recovery | Ohio Enhanced Service Reliability Plan        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 58   26  
Does not earns/earning a return | Approved for recovery | Plant Retirement Costs - Unrecovered Plant, Texas        
Regulatory Asset [Line Items]        
Remaining Recovery Period 21 years      
Total Noncurrent Regulatory Assets $ 45   45  
Does not earns/earning a return | Approved for recovery | Plant Retirement Costs - Unrecovered Plant, Texas | SOUTHWESTERN ELECTRIC POWER COMPANY        
Regulatory Asset [Line Items]        
Remaining Recovery Period 21 years      
Total Noncurrent Regulatory Assets $ 45   45  
Does not earns/earning a return | Approved for recovery | Smart Grid Costs        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 44   34  
Does not earns/earning a return | Approved for recovery | Renewable Resource Rider        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 38   0  
Does not earns/earning a return | Approved for recovery | Bad Debt Rider        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 35   22  
Does not earns/earning a return | Approved for recovery | West Virginia Environmental Compliance Surcharge        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 33   26  
Does not earns/earning a return | Approved for recovery | Postemployment Benefits        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 28   28  
Does not earns/earning a return | Approved for recovery | Fuel and Purchased Power Adjustment Rider        
Regulatory Asset [Line Items]        
Remaining Recovery Period 2 years      
Total Noncurrent Regulatory Assets $ 4   57  
Does not earns/earning a return | Approved for recovery | OVEC Purchased Power        
Regulatory Asset [Line Items]        
Total Noncurrent Regulatory Assets $ 0   $ 52