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Commitments, Guarantees and Contingencies (Details) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2017 | Jan. 31, 2017
Guarantor Obligations [Line Items] |  |
Guarantor obligations | $ 419,000,000 |
At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 11,000,000 |
Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 50,000,000 |
Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | $ 358,000,000 |
Curing period | 30 days |
Regulated |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | $ 143,000,000 |
Regulated | At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 0 |
Regulated | Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 50,000,000 |
Regulated | Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 93,000,000 |
FirstEnergy |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 7,000,000 |
FirstEnergy | At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 0 |
FirstEnergy | Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 0 |
FirstEnergy | Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 7,000,000 |
FES |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 241,000,000 |
FES | At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 8,000,000 |
FES | Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 0 |
FES | Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 233,000,000 |
FES | Surety Bond (Collateralized Amount) | Little Bull Run [Member] |  |
Guarantor Obligations [Line Items] |  |
Amount of surety bond |  | $ 169,000,000
AE Supply |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 28,000,000 |
AE Supply | At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 3,000,000 |
AE Supply | Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 0 |
AE Supply | Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | $ 25,000,000 |

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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248 + Details
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