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Commitments, Guarantees and Contingencies (Details Textuals)				3 Months Ended	9 Months Ended
	May 01, 2017 USD ($) installment	Dec. 22, 2016 T	Aug. 03, 2015 T	Mar. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) phase T	Dec. 31, 2016 USD ($)
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated					$ 3,300,000,000
New syndicated senior secured term loan facility					$ 412,000,000
Proposed goal to reduce CO2 pollution (percent)					90.00%
Nuclear plant decommissioning trusts					$ 2,632,000,000	$ 2,514,000,000
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					$ 131,000,000
Environmental liabilities former gas facilities					84,000,000
Nuclear Plant Matters
Guarantor Obligations [Line Items]
Nuclear plant decommissioning trusts					$ 2,600,000,000
Caa Compliance
Guarantor Obligations [Line Items]
Amount remaining under contract \| T					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
Settled Litigation \| Caa Compliance
Guarantor Obligations [Line Items]
Loss recognized in period				$ 55,000,000
Regulated Distribution
Guarantor Obligations [Line Items]
Company posted collateral related to net liability positions					$ 3,000,000
FES
Guarantor Obligations [Line Items]
Company posted collateral related to net liability positions					128,000,000
New syndicated senior secured term loan facility					54,000,000
Nuclear plant decommissioning trusts					1,823,000,000	$ 1,552,000,000
FES \| Nuclear Plant Matters
Guarantor Obligations [Line Items]
Nuclear plant decommissioning trusts					1,800,000,000
FES \| Settled Litigation \| Caa Compliance
Guarantor Obligations [Line Items]
Loss recognized in period				$ 55,000,000
FES \| Competitive Energy Services
Guarantor Obligations [Line Items]
New syndicated senior secured term loan facility					2,000,000
Global Holding \| Senior Secured Term Loan \| Senior Loans
Guarantor Obligations [Line Items]
New syndicated senior secured term loan facility					$ 300,000,000
Global Holding \| Senior Secured Term Loan \| Senior Loans \| Signal Peak, Global Rail and Affiliates
Guarantor Obligations [Line Items]
Investment ownership percentage					69.99%
FEV \| Senior Secured Term Loan \| Senior Loans \| Signal Peak \| Global Holding
Guarantor Obligations [Line Items]
Investment ownership percentage					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%
FG \| Settled Litigation \| Caa Compliance
Guarantor Obligations [Line Items]
Settlement amount	$ 109,000,000
Number of installment payments \| installment	3
AE Supply
Guarantor Obligations [Line Items]
Company posted collateral related to net liability positions					$ 2,000,000
New syndicated senior secured term loan facility					26,000,000
Minimum \| Clean Water Act
Guarantor Obligations [Line Items]
Capital investment required to install technology to meet TDS and Sulfate limits					150,000,000
Maximum \| Clean Water Act
Guarantor Obligations [Line Items]
Capital investment required to install technology to meet TDS and Sulfate limits					300,000,000
Certain Coal-Fired Power Plant \| FG \| Mercury and Air Toxic Standards
Guarantor Obligations [Line Items]
Minimum coal supply commitment (ton) \| T			3,500,000.0
Another Coal-Fired Power Plant \| FG \| 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					649,000,000
Subsidiaries
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated					1,900,000,000
Other Guarantee
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated					300,000,000
Other Assurances
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated					457,000,000
Line of Credit \| Revolving Credit Facility
Guarantor Obligations [Line Items]
Maximum amount borrowed under revolving credit facility					500,000,000
Line of Credit \| Revolving Credit Facility \| Nuclear Plant Matters
Guarantor Obligations [Line Items]
Maximum amount borrowed under revolving credit facility					500,000,000
NG \| Financial Guarantee \| FES \| Nuclear Plant Matters
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated					$ 400,000,000