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Asset Sales and Impairments (Details 1) |  |  |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 13, 2017 USD ($) | Oct. 20, 2017 | Aug. 30, 2017 USD ($) limited_guaranty Natural_gas_plant | Jul. 22, 2016 MW | Aug. 31, 2017 USD ($) Natural_gas_plant MW | Jan. 31, 2017 USD ($) MW | Dec. 31, 2017 USD ($) MW | Sep. 30, 2017 USD ($) | Jun. 30, 2017 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Sep. 30, 2016 USD ($) | Jun. 30, 2016 USD ($) | Mar. 31, 2016 USD ($) | Jun. 30, 2018 USD ($) | Dec. 31, 2017 USD ($) MW | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Mar. 06, 2017 USD ($) MW
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 42,000,000 |
Potential collateral obligations |  |  |  |  |  |  | $ 407,000,000 |  |  |  |  |  |  |  |  | $ 407,000,000 |  |  |
Impairments of long-lived assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,406,000,000 | $ 10,665,000,000 | 42,000,000 |
Impairment of assets and related charges (Note 2) |  |  |  |  |  |  | $ 2,244,000,000 | $ 31,000,000 | $ 131,000,000 | $ 0 | $ 9,218,000,000 | $ 0 | $ 1,447,000,000 | $ 0 |  | $ 2,406,000,000 | 10,665,000,000 | 42,000,000 |
Impairment |  |  |  |  |  |  |  |  |  |  |  |  | 800,000,000 |  |  |  | 800,000,000 |  |
Contract Termination |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring charges |  |  |  |  |  |  |  |  |  |  |  |  | 58,000,000 |  |  |  |  |  |
CES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets |  |  |  |  |  |  |  |  |  |  | 9,218,000,000 |  |  |  |  |  |  | 34,000,000 |
Plant generation capacity (in MW's) | MW |  |  |  |  |  |  | 12,303 |  |  |  |  |  |  |  |  | 12,303 |  |  |
Impairment of assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 193,000,000 |  |  |
Impairment of assets and related charges (Note 2) |  |  |  |  |  |  |  |  |  |  |  |  | 647,000,000 |  |  | $ 2,365,000,000 | $ 10,665,000,000 | 34,000,000 |
CES | Income Approach Valuation Technique | Goodwill |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discount rate (percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9.50% |  |
Terminal value of EBITDA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7.0 |  |
Regulated Distribution |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,000,000 |
Plant generation capacity (in MW's) | MW |  |  |  |  |  |  | 3,790 |  |  |  |  |  |  |  |  | 3,790 |  |  |
Potential collateral obligations |  |  |  |  |  |  | $ 148,000,000 |  |  |  |  |  |  |  |  | $ 148,000,000 |  |  |
Impairment of assets and related charges (Note 2) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 | $ 0 | 8,000,000 |
AE Supply |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential collateral obligations |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  | 2,000,000 |  |  |
FES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets |  |  |  |  |  |  | 2,045,000,000 |  |  |  |  |  |  |  |  |  |  | 33,000,000 |
Potential collateral obligations |  |  |  |  |  |  | 20,000,000 |  |  |  |  |  |  |  |  | 20,000,000 |  |  |
Impairments of long-lived assets |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,031,000,000 | 8,622,000,000 | 33,000,000 |
Impairment of assets and related charges (Note 2) |  |  |  |  |  |  | 2,031,000,000 | 0 | $ 0 | $ 0 | 8,082,000,000 | $ 0 | 540,000,000 | $ 0 |  | 2,031,000,000 | 8,622,000,000 | $ 33,000,000 |
Impairment |  |  |  |  |  |  |  |  |  |  |  |  | 23,000,000 |  |  |  | $ 23,000,000 |  |
FES | CES |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets |  |  |  |  |  |  | 2,000,000,000 |  |  |  | $ 8,082,000,000 |  |  |  |  |  |  |  |
Potential collateral obligations |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  | 2,000,000 |  |  |
Impairment of assets |  |  |  |  |  |  | 2,000,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets and related charges (Note 2) |  |  |  |  |  |  |  |  |  |  |  |  | $ 517,000,000 |  |  |  |  |  |
MAIT |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairments of long-lived assets |  |  |  |  |  |  |  | $ 13,000,000 |  |  |  |  |  |  |  |  |  |  |
Pleasants Power Station |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment of assets |  |  |  |  |  |  | 120,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Plant generation capacity (in MW's) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,300
Assets purchase agreement consideration to be received |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 195,000,000
Carrying value of power station |  |  |  |  |  |  | $ 75,000,000 |  |  |  |  |  |  |  |  | $ 75,000,000 |  |  |
Bay Shore Unit 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant capacity (in MW's) | MW |  |  |  | 136 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sammis Power Plant Units 1-4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant capacity (in MW's) | MW |  |  |  | 720 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant generation capacity (in MW's) | MW |  |  |  |  | 1,615 |  | 756 |  |  |  |  |  |  |  |  | 756 |  |  |
Plant capacity (in MW's) | MW |  |  |  |  |  | 1,615 |  |  |  |  |  |  |  |  |  |  |  |  |
Cash purchase price |  |  |  |  | $ 825,000,000 | $ 825,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Number of limited guaranties | limited_guaranty |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of guaranties |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase Agreement with Subsidiary of LS Power | AE Supply |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of gas generating plants | Natural_gas_plant |  |  | 4 |  | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discharge of note indenture |  |  | $ 305,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Make-whole premiums |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 95,000,000 |  |  |
Purchase Agreement with Subsidiary of LS Power | AGC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Plant ownership percentage |  | 59.00% | 59.00% |  | 59.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Make-whole premiums |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 95,000,000 |  |  |
Purchase Agreement with Subsidiary of LS Power | Natural Gas Generating Plants |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash purchase price | $ 388,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Held-for-sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Assets held-for-sale |  |  |  |  |  |  | $ 354,000,000 |  |  |  |  |  |  |  |  | 354,000,000 |  |  |
Investments |  |  |  |  |  |  | 19,000,000 |  |  |  |  |  |  |  |  | 19,000,000 |  |  |
Materials and supplies inventory |  |  |  |  |  |  | 2,000,000 |  |  |  |  |  |  |  |  | 2,000,000 |  |  |
Forecast | Purchase Agreement with Subsidiary of LS Power | Bath County Hydroelectric Power Station and Buchanan Generating Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 375,000,000 |  |  |  |
FE |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential collateral obligations |  |  |  |  |  |  | 237,000,000 |  |  |  |  |  |  |  |  | $ 237,000,000 |  |  |
FE | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential collateral obligations | $ 555,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase Agreement Guarantee, Breaches of Covenants and Indebtedness | FE | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Term of guaranties | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential collateral obligations | $ 463,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase Agreement Guarantee, Breaches of Non-fundamental Representations | FE | Purchase Agreement with Subsidiary of LS Power |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential collateral obligations | $ 92,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes | Purchase Agreement with Subsidiary of LS Power | AGC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discharge of note indenture |  |  | $ 100,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PCRB | Purchase Agreement with Subsidiary of LS Power | AE Supply |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Discharge of note indenture |  |  | $ 142,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FERC | JCP&L |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairments of long-lived assets |  |  |  |  |  |  | $ 28,000,000 |  |  |  |  |  |  |  |  |  |  |  |

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