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Commitments, Guarantees and Contingencies (Details Textuals) |  |  | 1 Months Ended | 6 Months Ended | 9 Months Ended | 12 Months Ended | 54 Months Ended |  |
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Oct. 01, 2015 | Aug. 03, 2015 T | Jun. 30, 2014 | May 31, 2014 | Jun. 30, 2016 USD ($) phases T | Sep. 30, 2015 | Dec. 31, 2014 USD ($) | Jun. 30, 2016 USD ($) T | Dec. 31, 2015 USD ($) | Oct. 31, 2012 USD ($)
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding guarantees and other assurances aggregated |  |  |  |  | $ 3,500,000,000 |  |  | $ 3,500,000,000 |  |
New syndicated senior secured term loan facility |  |  |  |  | $ 379,000,000 |  |  | 379,000,000 |  |
Proposed goal to reduce CO2 pollution (percent) |  |  |  |  | 90.00% |  |  |  |  |
Nuclear plant decommissioning trusts |  |  |  |  | $ 2,456,000,000 |  |  | 2,456,000,000 | $ 2,282,000,000 |
Clean Water Act |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Waste water discharge permit renewal cycle |  |  |  |  |  | 5 years |  |  |  |
Regulation of Waste Disposal |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Bond closure and post closure period |  |  |  |  | 45 years |  |  |  |  |
Period to complete closure |  |  |  |  | 12 years |  |  |  |  |
Accrual for environmental loss contingencies |  |  |  |  | $ 124,000,000 |  |  | 124,000,000 |  |
Environmental liabilities former gas facilities |  |  |  |  | 89,000,000 |  |  | 89,000,000 |  |
Nuclear Plant Matters |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Nuclear plant decommissioning trusts |  |  |  |  | 2,500,000,000 |  |  | 2,500,000,000 |  |
Parental guarantee |  |  |  |  | $ 24,500,000 |  |  | 24,500,000 |  |
Renewal length of operating license for Davis-Besse Nuclear Power Station |  |  |  |  | 20 years |  |  |  |  |
Caa Compliance |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Loss in period |  |  |  |  |  |  |  | $ 253,000,000 |  |
Amount remaining under contract | T |  |  |  |  | 5,500,000 |  |  | 5,500,000 |  |
National Ambient Air Quality Standards |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Capping of SO2 emissions under CSAPR | T |  |  |  |  | 2,400,000 |  |  |  |  |
Capping of NOx emissions under CSAPR | T |  |  |  |  | 1,200,000 |  |  |  |  |
National Ambient Air Quality Standards | CSAPR |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides | phases |  |  |  |  | 2 |  |  |  |  |
Hazardous Air Pollutant Emissions |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Potential cost of compliance, MATS |  |  |  |  | $ 345,000,000 |  |  | $ 345,000,000 |  |
Climate Change |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Annual percentage that fish impingement should be reduced to, per CWA |  |  |  | 12.00% |  |  |  |  |  |
Regulated Distribution | Caa Compliance |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Loss in period |  |  |  |  |  |  |  | 145,000,000 |  |
Regulated Distribution | Hazardous Air Pollutant Emissions |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Potential cost of compliance, MATS |  |  |  |  | 177,000,000 |  |  | 177,000,000 |  |
Competitive Energy Services | Caa Compliance |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Loss in period |  |  |  |  |  |  |  | 108,000,000 |  |
Competitive Energy Services | Hazardous Air Pollutant Emissions |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Potential cost of compliance, MATS |  |  |  |  | 168,000,000 |  |  | 168,000,000 |  |
FES |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Company posted collateral related to net liability positions |  |  |  |  | 145,000,000 |  |  | 145,000,000 |  |
Settlement amount |  |  |  |  |  |  | $ 70,000,000 |  |  |
Nuclear plant decommissioning trusts |  |  |  |  | 1,510,000,000 |  |  | 1,510,000,000 | $ 1,327,000,000 |
Global Holding | Senior Secured Term Loan | Senior Loans |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
New syndicated senior secured term loan facility |  |  |  |  | $ 300,000,000 |  |  | $ 300,000,000 |  | $ 350,000,000
Global Holding | Senior Secured Term Loan | Senior Loans | Signal Peak, Global Rail and Affiliates |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Investment ownership percentage |  |  |  |  | 69.99% |  |  | 69.99% |  |
FEV | Senior Secured Term Loan | Senior Loans | Signal Peak | Global Holding |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Investment ownership percentage |  |  |  |  | 33.33% |  |  | 33.33% |  |
WMB Marketing Ventures, LLC | Senior Secured Term Loan | Senior Loans | Signal Peak | Global Holding |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Investment ownership percentage |  |  |  |  | 33.33% |  |  | 33.33% |  |
Environmental Protection Agency | Caa Compliance |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Period of time to implement plan | 3 years |  |  |  |  |  |  |  |  |
Minimum | Clean Water Act |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Maximum capital investment required to install technology to meet TDS and Sulfate limits |  |  |  |  | $ 150,000,000 |  |  |  |  |
Maximum | Clean Water Act |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Maximum capital investment required to install technology to meet TDS and Sulfate limits |  |  |  |  | 300,000,000 |  |  |  |  |
Maximum | State and Local Agencies | Climate Change |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Potential MATS extension period |  |  | 2 years |  |  |  |  |  |  |
Certain Coal-Fired Power Plant | FirstEnergy Generation LLC | Mercury and Air Toxic Standards |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Minimum coal supply commitment (ton) | T |  | 3,500,000.0 |  |  |  |  |  |  |  |
Another Coal-Fired Power Plant | FirstEnergy Generation LLC | Mercury and Air Toxic Standards |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Minimum coal supply commitment (ton) | T |  | 2,500,000.0 |  |  |  |  |  |  |  |
FirstEnergy |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding guarantees and other assurances aggregated |  |  |  |  | 590,000,000 |  |  | $ 590,000,000 |  |
Subsidiaries |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding guarantees and other assurances aggregated |  |  |  |  | 2,000,000,000 |  |  | 2,000,000,000 |  |
Other Guarantee |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding guarantees and other assurances aggregated |  |  |  |  | 300,000,000 |  |  | 300,000,000 |  |
Other Assurances |  |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding guarantees and other assurances aggregated |  |  |  |  | $ 597,000,000 |  |  | $ 597,000,000 |  |

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