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Commitments, Guarantees and Contingencies (Details Textuals) |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
May 01, 2017 USD ($) installment | Oct. 01, 2015 | Aug. 03, 2015 T | Jun. 30, 2014 | Mar. 31, 2017 USD ($) | Jun. 30, 2017 USD ($) phase T | Jun. 30, 2016 | Dec. 31, 2016 USD ($) | Oct. 31, 2012 USD ($)
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |
Outstanding guarantees and other assurances aggregated |  |  |  |  |  | $ 3,300,000,000 |  |  |
New syndicated senior secured term loan facility |  |  |  |  |  | $ 420,000,000 |  |  |
Proposed goal to reduce CO2 pollution (percent) |  |  |  |  |  | 90.00% |  |  |
Nuclear plant decommissioning trusts |  |  |  |  |  | $ 2,588,000,000 |  | $ 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 |  |  |  |  |  | $ 4,000,000 |  |  |
FES |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |
Company posted collateral related to net liability positions |  |  |  |  |  | 123,000,000 |  |  |
New syndicated senior secured term loan facility |  |  |  |  |  | 71,000,000 |  |  |
Nuclear plant decommissioning trusts |  |  |  |  |  | 1,793,000,000 |  | 1,552,000,000 |
FES | Caa Compliance |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |
Annual contested damage claim |  |  |  |  |  | $ 70,000,000 |  |  |
Period of annual contested damage claim |  |  |  |  |  | 11 years |  |  |
FES | 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 |  |  | $ 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% |  |  |
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 |  |  |  |  |  |  |  |
AE Supply |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |
Company posted collateral related to net liability positions |  |  |  |  |  | $ 0 |  |  |
New syndicated senior secured term loan facility |  |  |  |  |  | 27,000,000 |  |  |
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 |  |  |
Minimum | FES | Caa Compliance |  |  |  |  |  |  |  |  |
Guarantor Obligations [Line Items] |  |  |  |  |  |  |  |  |
Number of installment payments | installment | 3 |  |  |  |  |  |  |  |
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 | 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 |  |  |  |  |  | 466,000,000 |  |  |
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 |

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