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Short-Term Borrowings and Bank Lines of Credit (Details) - USD ($) | Jan. 31, 2017 | Dec. 31, 2016 | Dec. 06, 2016 | Dec. 05, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
--- | --- | --- | --- | --- | --- | --- | ---
Short-term Debt [Line Items] |  |  |  |  |  |  |
Cash and Cash Equivalents, at Carrying Value |  | $ 199,000,000 |  |  | $ 131,000,000 | $ 85,000,000 | $ 218,000,000
Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility | $ 5,000,000,000 |  |  |  |  |  |
Available Liquidity | 2,341,000,000 |  |  |  |  |  |
Cash, Available Liquidity | 308,000,000 |  |  |  |  |  |
Total Available Liquidity | 2,649,000,000 |  |  |  |  |  |
FirstEnergy |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility |  | 4,000,000,000 |  |  |  |  |
FirstEnergy | Line of Credit | Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Available Liquidity | 1,341,000,000 |  |  |  |  |  |
FET |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility |  | 1,000,000,000 |  |  |  |  |
FET | Line of Credit | Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Available Liquidity | 1,000,000,000 |  |  |  |  |  |
FES |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Cash and Cash Equivalents, at Carrying Value |  | 2,000,000 |  |  | $ 2,000,000 | $ 2,000,000 | $ 2,000,000
FES | Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility | 500,000,000 |  |  |  |  |  |
Total Available Liquidity | 502,000,000 |  |  |  |  |  |
FES | Line of Credit | Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Available Liquidity | 500,000,000 |  |  |  |  |  |
Revolving Credit Facility | Line of Credit |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility |  | $ 500,000,000 | $ 4,000,000,000 | $ 3,500,000,000.0 |  |  |
Revolving Credit Facility | Line of Credit | Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility | 5,000,000,000 |  |  |  |  |  |
Revolving Credit Facility | FirstEnergy | Line of Credit | Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility | 4,000,000,000 |  |  |  |  |  |
Revolving Credit Facility | FET | Line of Credit |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility |  |  | $ 1,000,000,000 | 1,000,000,000 |  |  |
Revolving Credit Facility | FET | Line of Credit | Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility | 1,000,000,000 |  |  |  |  |  |
Revolving Credit Facility | FES | Line of Credit |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility |  |  |  | $ 900,000,000 |  |  |
Revolving Credit Facility | FES | Line of Credit | Subsequent Event |  |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |  |
Maximum amount borrowed under revolving credit facility | $ 500,000,000 |  |  |  |  |  |

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