Commitments, Guarantees and Contingencies (Details Textuals)
 1 Months Ended 9 Months Ended 12 Months Ended 57 Months Ended
Oct. 01, 2015
Aug. 03, 2015
T
Jun. 30, 2014
May 31, 2014
Sep. 30, 2016
USD ($)
phase
T
Sep. 30, 2015
Dec. 31, 2014
USD ($)
Sep. 30, 2016
USD ($)
T
Nov. 04, 2016
USD ($)
Aug. 01, 2016
USD ($)
Dec. 31, 2015
USD ($)
Oct. 31, 2012
USD ($)
Guarantor Obligations [Line Items]                        
Outstanding guarantees and other assurances aggregated         $ 3,400,000,000     $ 3,400,000,000        
New syndicated senior secured term loan facility         $ 499,000,000     499,000,000        
Proposed goal to reduce CO2 pollution (percent)         90.00%              
Nuclear plant decommissioning trusts         $ 2,502,000,000     2,502,000,000     $ 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         $ 121,000,000     121,000,000        
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               $ 267,000,000        
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 | phase         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               150,000,000        
Regulated Distribution | Hazardous Air Pollutant Emissions                        
Guarantor Obligations [Line Items]                        
Potential cost of compliance, MATS         177,000,000     177,000,000        
Competitive Energy Services                        
Guarantor Obligations [Line Items]                        
New syndicated senior secured term loan facility         355,000,000     355,000,000        
Competitive Energy Services | Caa Compliance                        
Guarantor Obligations [Line Items]                        
Loss in period               117,000,000        
Competitive Energy Services | Hazardous Air Pollutant Emissions                        
Guarantor Obligations [Line Items]                        
Potential cost of compliance, MATS         168,000,000     168,000,000        
FES and AE Supply | Competitive Energy Services                        
Guarantor Obligations [Line Items]                        
Company posted collateral related to net liability positions                   $ 53,000,000    
Additional collateral posted or accelerated payments         81,000,000     81,000,000        
FES                        
Guarantor Obligations [Line Items]                        
Company posted collateral related to net liability positions         193,000,000     193,000,000        
Settlement amount             $ 70,000,000          
Nuclear plant decommissioning trusts         1,542,000,000     1,542,000,000     $ 1,327,000,000  
FES | Caa Compliance                        
Guarantor Obligations [Line Items]                        
Annual contested damage claim         $ 70,000,000              
Period of annual contested damage claim         11 years              
FES | Competitive Energy Services                        
Guarantor Obligations [Line Items]                        
Additional collateral posted or accelerated payments                 $ 355,000,000      
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%        
AE Supply                        
Guarantor Obligations [Line Items]                        
Company posted collateral related to net liability positions         $ 4,000,000     $ 4,000,000        
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         584,000,000     584,000,000        
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         $ 504,000,000     $ 504,000,000