v3.26.3
ORGANIZATION AND BASIS OF PRESENTATION (Details)
3 Months Ended 9 Months Ended
Feb. 13, 2026
Feb. 12, 2026
USD ($)
Feb. 26, 2025
USD ($)
transmission_project
Sep. 30, 2026
USD ($)
mi
kV
Jun. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
segment
mi
kV
Sep. 30, 2025
USD ($)
Feb. 21, 2025
Mar. 25, 2024
director
May 31, 2022
Regulatory Asset [Line Items]                      
Service area | mi       12,515     12,515        
Nominal voltage (in kV) | kV       500     500        
Nominal voltage (in kV) | kV       345     345        
Nominal voltage (in kV) | kV       230     230        
Nominal voltage (in kV) | kV       138     138        
Nominal voltage (in kV) | kV       115     115        
Nominal voltage (in kV) | kV       69     69        
Nominal voltage (in kV) | kV       46     46        
Number of directors | director                   5  
Impairment of goodwill             $ 0        
Capitalized cost of equity       $ 20,000,000   $ 16,000,000 56,000,000 $ 42,000,000      
Capitalized interest       $ 6,000,000   $ 7,000,000 17,000,000 15,000,000      
Proceeds from divestiture of interest in joint venture             $ 21,000,000 $ 0      
Number of operating segments | segment             1        
MAIT | Common Class A                      
Regulatory Asset [Line Items]                      
Ownership percentage by parent                   100.00%  
MAIT | Common Class B                      
Regulatory Asset [Line Items]                      
Ownership percentage by parent                   100.00%  
Equity contribution from FE | FET                      
Regulatory Asset [Line Items]                      
Ownership percentage by parent                   50.10%  
FET | Grid Growth                      
Regulatory Asset [Line Items]                      
Ownership interest 50.00%                    
Transource | Grid Growth                      
Regulatory Asset [Line Items]                      
Ownership interest 50.00%                    
Grid Growth | PJM Interconnection, LLC | PJM 2025 RTEP Window 1                      
Regulatory Asset [Line Items]                      
Transmission solutions to the reliability issues   $ 1,000,000,000                  
Grid Growth | Grid Growth EHV Holdings, LLC                      
Regulatory Asset [Line Items]                      
Ownership interest 80.00%                    
FET | Brookfield                      
Regulatory Asset [Line Items]                      
Sale of ownership interest by parent                   30.00%  
Valley Link                      
Regulatory Asset [Line Items]                      
Equity method investment, ownership percentage                 34.00%    
Valley Link | PJM Interconnection, LLC | PJM 2024 RTEP Window 1                      
Regulatory Asset [Line Items]                      
Number of transmission projects | transmission_project     2                
Transmission solutions to the reliability issues     $ 3,000,000,000                
Valley Link | FET | PJM Interconnection, LLC | PJM 2024 RTEP Window 1                      
Regulatory Asset [Line Items]                      
Transmission solutions to the reliability issues     $ 1,000,000,000                
Valley Link | Dominion HV                      
Regulatory Asset [Line Items]                      
Equity method investment, ownership percentage                 30.00%    
Valley Link | Transource Energy, LLC                      
Regulatory Asset [Line Items]                      
Equity method investment, ownership percentage                 36.00%    
Grid Growth | PJM Interconnection, LLC | PJM 2025 RTEP Window 1                      
Regulatory Asset [Line Items]                      
Transmission solutions to the reliability issues   $ 448,000,000                  
Path WV | Variable Interest Entity, Not Primary Beneficiary                      
Regulatory Asset [Line Items]                      
Variable interest entities percentage of high voltage transmission line project owned by variable interest entity one in joint venture party two       50.00%     50.00%        
Proceeds from divestiture of interest in joint venture         $ 21,000,000            
North American Transmission Company II LLC | FET | Brookfield                      
Regulatory Asset [Line Items]                      
Equity method investment, ownership percentage                   49.90% 19.90%
Brookfield                      
Regulatory Asset [Line Items]                      
Number of directors | director                   2  
Equity contribution from FE                      
Regulatory Asset [Line Items]                      
Number of directors | director                   3  
MAIT | Common Class B                      
Regulatory Asset [Line Items]                      
Special purpose membership interest held, percentage of distributions       1     1