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Organization and Basis of Presentation (Details)
customer in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2020
USD ($)
company
agreement
transmission_center
MW
Sep. 30, 2019
USD ($)
Sep. 30, 2020
USD ($)
company
agreement
customer
transmission_center
mi
MW
Sep. 30, 2019
USD ($)
Nov. 17, 2020
USD ($)
Property, Plant and Equipment [Line Items]          
Length of transmission lines | mi     24,500    
Number of regional transmission centers | transmission_center 2   2    
Capitalized cost of equity $ 13,000,000 $ 12,000,000 $ 36,000,000 $ 34,000,000  
Capitalized interest 8,000,000 $ 7,000,000 21,000,000 $ 19,000,000  
Incremental increase to uncollectible expense due to Covid-19 20,000,000   63,000,000    
Revolving Credit Facility | Line of Credit          
Property, Plant and Equipment [Line Items]          
Maximum amount borrowed under revolving credit facility $ 3,500,000,000   $ 3,500,000,000    
Number of agreements | agreement 2   2    
Revolving Credit Facility | Line of Credit | FirstEnergy          
Property, Plant and Equipment [Line Items]          
Maximum amount borrowed under revolving credit facility $ 2,500,000,000   $ 2,500,000,000    
Revolving Credit Facility | Line of Credit | FirstEnergy | Subsequent Event          
Property, Plant and Equipment [Line Items]          
Maximum amount borrowed under revolving credit facility         $ 1,500,000,000
Revolving Credit Facility | Line of Credit | FET Sub-limits          
Property, Plant and Equipment [Line Items]          
Maximum amount borrowed under revolving credit facility 1,000,000,000.0   $ 1,000,000,000.0    
Revolving Credit Facility | Line of Credit | Parent, the Utilities, FET and Certain Subsidiaries [Member]          
Property, Plant and Equipment [Line Items]          
Debt term     5 years    
Future Recovery of Incremental Costs          
Property, Plant and Equipment [Line Items]          
Incremental increase to uncollectible expense due to Covid-19 $ 13,000,000   $ 40,000,000    
Regulated Distribution          
Property, Plant and Equipment [Line Items]          
Number of existing utility operating companies | company 10   10    
Number of customers served by utility operating companies | customer     6    
Plant capacity (in MW's) | MW 3,790   3,790    
Regulated Distribution | Yard Creek Generating Plant          
Property, Plant and Equipment [Line Items]          
Plant capacity (in MW's) | MW 210   210