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