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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 |

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