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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled.

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The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount awarded to other party in judgment or settlement of litigation.

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The amount of cash paid for the settlement of litigation or for other legal issues during the period.

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Commitments, Guarantees and Contingencies (Details Textuals)				3 Months Ended
	Apr. 06, 2018 USD ($)	Feb. 18, 2018 USD ($)	May 01, 2017 USD ($) installment	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated				$ 1,900,000,000
New syndicated senior secured term loan facility				$ 393,000,000
Curing period				30 days
Settlement amount awarded to other party		$ 93,000,000
Proposed goal to reduce CO2 pollution (percent)				90.00%
Nuclear plant decommissioning trusts				$ 800,000,000	$ 822,000,000
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				$ 125,000,000
Environmental liabilities former gas facilities				85,000,000
Nuclear Plant Matters
Guarantor Obligations [Line Items]
Nuclear plant decommissioning trusts				800,000,000
Regulated Distribution
Guarantor Obligations [Line Items]
Company posted collateral related to net liability positions				$ 6,000,000
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				$ 0
New syndicated senior secured term loan facility				2,000,000
Settlement amount awarded to other party		$ 93,000,000
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
FES and FENOC
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated				484,000,000
FirstEnergy
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated				1,007,000,000
Other Guarantee
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated				255,000,000
Other Assurances
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated				178,000,000
Little Bull Run \| Line of Credit \| Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Maximum amount borrowed under revolving credit facility				169,000,000
Hatfield Ferry \| Line of Credit \| Surety Bond (Collateralized Amount)
Guarantor Obligations [Line Items]
Maximum amount borrowed under revolving credit facility				$ 31,000,000
Subsequent Event \| FG \| Settled Litigation \| Caa Compliance
Guarantor Obligations [Line Items]
Settlement payments	$ 72,000,000