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Organization and Basis of Presentation - Narrative (Details)
mi in Thousands, customer in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2021
USD ($)
company
agreement
transmissionCenter
MW
Jun. 30, 2020
USD ($)
Jun. 30, 2021
USD ($)
customer
transmissionCenter
company
agreement
mi
MW
Jun. 30, 2020
USD ($)
Property, Plant and Equipment [Line Items]        
Length of transmission lines | mi     24  
Number of regional transmission centers | transmissionCenter 2   2  
Capitalized cost of equity $ 14,000,000 $ 12,000,000 $ 21,000,000 $ 23,000,000
Capitalized interest $ 7,000,000 $ 6,000,000 $ 13,000,000 $ 13,000,000
Revolving Credit Facility | Line of Credit        
Property, Plant and Equipment [Line Items]        
Number of agreements | agreement 2   2  
Maximum amount borrowed under revolving credit facility $ 3,500,000,000   $ 3,500,000,000  
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 | 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  
PN | Waverly, New York        
Property, Plant and Equipment [Line Items]        
Number of customers served by utility operating companies | customer     4  
Parent, the Utilities, FET and Certain Subsidiaries | Revolving Credit Facility | Line of Credit        
Property, Plant and Equipment [Line Items]        
Debt term     5 years  
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     6,000  
Plant capacity (in MW's) | MW 3,580   3,580