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Commitments, Guarantees and Contingencies (Details) - USD ($) | 9 Months Ended |
--- | --- | ---
Sep. 30, 2017 | Jan. 31, 2017
Guarantor Obligations [Line Items] |  |
Guarantor obligations | $ 412,000,000 |
At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 8,000,000 |
Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 42,000,000 |
Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | $ 362,000,000 |
Curing period | 30 days |
Regulated |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | $ 147,000,000 |
Regulated | At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 0 |
Regulated | Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 42,000,000 |
Regulated | Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 105,000,000 |
FirstEnergy |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 185,000,000 |
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 | 185,000,000 |
FES |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 54,000,000 |
FES | At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 6,000,000 |
FES | Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 0 |
FES | Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 48,000,000 |
FES | Surety Bond (Collateralized Amount) | Little Bull Run | PA DEP |  |
Guarantor Obligations [Line Items] |  |
Amount of surety bond |  | $ 169,000,000
AE Supply |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 26,000,000 |
AE Supply | At Current Credit Rating |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 2,000,000 |
AE Supply | Upon Further Downgrade |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | 0 |
AE Supply | Surety Bond (Collateralized Amount) |  |
Guarantor Obligations [Line Items] |  |
Guarantor obligations | $ 24,000,000 |

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