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CAPITALIZATION - Narrative (Details) |  |  |  | 3 Months Ended | 12 Months Ended |  |  |  |  |  |  |
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Dec. 15, 2020 $ / shares | Apr. 20, 2020 USD ($) | Feb. 20, 2020 USD ($) series | Dec. 31, 2020 USD ($) $ / shares shares | Sep. 30, 2020 $ / shares | Jun. 30, 2020 $ / shares | Mar. 31, 2020 USD ($) $ / shares | Dec. 31, 2019 USD ($) $ / shares shares | Sep. 30, 2019 $ / shares | Jun. 30, 2019 $ / shares | Mar. 31, 2019 $ / shares | Dec. 31, 2020 USD ($) subsidiary $ / shares shares | Dec. 31, 2019 USD ($) $ / shares shares | Dec. 31, 2018 USD ($) $ / shares shares | Jul. 20, 2020 USD ($) | Jun. 29, 2020 USD ($) | Jun. 08, 2020 USD ($) series | Feb. 27, 2020 USD ($) | Jan. 31, 2018 USD ($) $ / shares shares | Jan. 22, 2018 USD ($) $ / shares shares | Jun. 30, 2013 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Retained earnings (accumulated deficit) |  |  |  | $ (2,888,000,000) |  |  |  | $ (3,967,000,000) |  |  |  | $ (2,888,000,000) | $ (3,967,000,000) |  |  |  |  |  |  |  |
Dividends declared (in dollars per share) | $ / shares | $ 0.39 |  |  |  |  |  |  |  |  |  |  | $ 1.56 | $ 1.53 | $ 1.82 |  |  |  |  |  |  |
Common stock dividends per share paid, in dollars per share | $ / shares |  |  |  | $ 0.39 | $ 0.39 | $ 0.39 | $ 0.39 | $ 0.38 | $ 0.38 | $ 0.38 | $ 0.38 |  |  |  |  |  |  |  |  |  |
FERC-defined equity to total capitalization ratio |  |  |  |  |  |  |  |  |  |  |  | 35.00% |  |  |  |  |  |  |  |  |
Common stock, par value (in dollars per share) | $ / shares |  |  |  | $ 0.10 |  |  |  | $ 0.10 |  |  |  | $ 0.10 | $ 0.10 |  |  |  |  |  |  |  |
Amount of private placement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 850,000,000 |
Preferred shares, outstanding (in shares) | shares |  |  |  | 0 |  |  |  | 0 |  |  |  | 0 | 0 |  |  |  |  |  |  |  |
Preference shares outstanding (in shares) | shares |  |  |  | 0 |  |  |  | 0 |  |  |  | 0 | 0 |  |  |  |  |  |  |  |
Transition bond outstanding |  |  |  | $ 9,000,000 |  |  |  | $ 25,000,000 |  |  |  | $ 9,000,000 | $ 25,000,000 |  |  |  |  |  |  |  |
Preferred stock, par value (in dollars per share) | $ / shares |  |  |  | $ 100 |  |  |  |  |  |  |  | $ 100 |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  |  |  |  |  | $ 1,114,000,000 | 789,000,000 | $ 2,608,000,000 |  |  |  |  |  |  |
Number of subsidiaries that issued environmental control bonds | subsidiary |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |
Environmental control bonds outstanding |  |  |  | $ 300,000,000 |  |  |  | 333,000,000 |  |  |  | $ 300,000,000 | $ 333,000,000 |  |  |  |  |  |  |  |
2021 |  |  |  | 132,000,000 |  |  |  |  |  |  |  | 132,000,000 |  |  |  |  |  |  |  |  |
Principal default amount specified in debt covenants |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |
Common Stock Purchase Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of shares issued | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30,120,482 |
Common stock, par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0.10 |
Registered Shareholders, Directors and Employees of Subsidiaries |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Investment Plan and certain share-based benefit plans (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 | 3,000,000 | 3,200,000 |  |  |  |  |  |  |
Series A Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Preferred stock shares issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,616,000 |  |
Preferred stock, par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100 |  |
Amount of preferred stock investment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,620,000,000 |  |
Phase In Recovery Bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt and other long-term obligations |  |  |  | 245,000,000 |  |  |  | $ 268,000,000 |  |  |  | $ 245,000,000 | $ 268,000,000 |  |  |  |  |  |  |  |
Senior Notes | $750 Million Senior Unsecured Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 750,000,000 |  |  |  |
Number of debt series | series |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |
Senior Notes | 1.60% Senior A Notes Due 2026 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 300,000,000 |  |  |  |
Interest rate (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.60% |  |  |  |
Senior Notes | 2.250% Senior B Notes Due 2030 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 450,000,000 |  |  |  |
Interest rate (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.25% |  |  |  |
Senior Notes | $1.75 Billion Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  | $ 1,750,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of debt series | series |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes | 2.050% Series A Senior Notes Due 2025 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  | $ 300,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate (percent) |  |  | 2.05% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes | 2.650% Series B Senior Notes Due 2030 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  | $ 600,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate (percent) |  |  | 2.65% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes | 3.400% Series C Senior Notes Due 2050 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  | $ 850,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate (percent) |  |  | 3.40% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term Loan | $750M Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  | $ 750,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt term |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term Loan | $1B Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  | $ 1,000,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  | $ 250,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt term |  |  | 364 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Investment Plan and certain share-based benefit plans (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  | 2,000,000 | 3,000,000 | 4,000,000 |  |  |  |  |  |  |
Amount of private placement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,000,000 |
Number of shares issued | shares |  |  |  |  |  |  |  |  |  |  |  |  | 25,696,168 | 33,238,910 |  |  |  |  |  |  |
Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares converted | shares |  |  |  |  |  |  |  |  |  |  |  |  | 704,589 | 911,411 |  |  |  |  |  |  |
Preferred Stock | Series A Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of preferred stock investment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 162,000,000 |  |
OPIC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of private placement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 847,000,000 |
OPIC | Series A Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount of preferred stock investment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,460,000,000 |  |
PN | Senior Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  | $ 125,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PN | Senior Notes | 3.61% Senior Unsecured Notes Due 2032 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate (percent) |  | 3.61% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PN | Senior Notes | 3.71% Senior Notes Due 2035 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate (percent) |  | 3.71% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  | $ 125,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PN | Senior Notes | 5.20% Senior Notes Due 2020 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  | $ 250,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate (percent) |  | 5.20% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
MP | PCRB |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2021 |  |  |  | $ 74,000,000 |  |  |  |  |  |  |  | $ 74,000,000 |  |  |  |  |  |  |  |  |
MAIT | Senior Notes | 3.60 Percent Senior Notes Due 2032 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  | $ 125,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate (percent) |  |  |  |  |  |  | 3.60% |  |  |  |  |  |  |  |  |  |  |  |  |  |
MAIT | Senior Notes | 3.70% Senior Notes Due 2035 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  | $ 125,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rate (percent) |  |  |  |  |  |  | 3.70% |  |  |  |  |  |  |  |  |  |  |  |  |  |
PE | FMBs | 2.67% First Mortgage Bond Due 2032 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 75,000,000 |  |  |  |  |
Interest rate (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.67% |  |  |  |  |
PE | FMBs | 3.43% First Mortgage Bonds Due 2051 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |
Interest rate (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.43% |  |  |  |  |
CEI | Senior Notes | 2.77% Senior Notes Due 2034 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 150,000,000 |  |  |  |  |  |
Interest rate (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.77% |  |  |  |  |  |
CEI | Senior Notes | 3.23% Senior Notes Due 2040 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000 |  |  |  |  |  |
Interest rate (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.23% |  |  |  |  |  |
FES | FES Key Creditor Groups | Affiliates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount paid to settle claims |  |  | $ 853,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FES | IT Access Agreement | Affiliates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount paid to settle claims |  |  | $ 125,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 125,000,000 |  |  |
Ohio Funding Companies |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate annual servicing fees receivable for phase-in recovery bonds |  |  |  |  |  |  |  |  |  |  |  | $ 445,000 |  |  |  |  |  |  |  |  |
Ohio Funding Companies | Phase In Recovery Bonds |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount of loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 445,000,000
AGC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FERC-defined equity to total capitalization ratio |  |  |  |  |  |  |  |  |  |  |  | 45.00% |  |  |  |  |  |  |  |  |

X
- Definition Debt Instruments, Number of Debt Series + References No definition available. + Details
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Namespace Prefix: | fe_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Minimum Equity To Total Capitalization Ratio To Be Maintained For Payment Of Capital Dividend + References No definition available. + Details
Name: | fe_MinimumEquityToTotalCapitalizationRatioToBeMaintainedForPaymentOfCapitalDividend
Namespace Prefix: | fe_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number Of Subsidiaries That Issued Environmental Control Bonds + References No definition available. + Details
Name: | fe_NumberOfSubsidiariesThatIssuedEnvironmentalControlBonds
Namespace Prefix: | fe_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
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