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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2017
Asset Retirement Obligation [Abstract] |
Fair values of the decommissioning trust assets | The fair values of the decommissioning trust assets as of December 31, 2017 and 2016 were as follows:
|  | 2017 |  | 2016
|  | (In millions)
FirstEnergy |  | $ | 2,678 |  |  | $ | 2,514 |
FES |  | $ | 1,856 |  |  | $ | 1,552 |
Changes to the asset retirement obligations | The following table summarizes the changes to the ARO balances during 2017 and 2016:
ARO Reconciliation |  | FirstEnergy |  | FES
|  | (In millions)
Balance, January 1, 2016 |  | $ | 1,410 |  |  | $ | 831 |
Liabilities settled |  | (27 | ) |  | (18 | )
Accretion |  | 95 |  |  | 56 |
Liabilities Incurred |  | 4 |  |  | 32 |
Balance, December 31, 2016 |  | $ | 1,482 |  |  | $ | 901 |
Changes in timing of estimated cash flows (1) |  | 944 |  |  | 944 |
Liabilities settled |  | (12 | ) |  | (11 | )
Accretion |  | 101 |  |  | 62 |
Liabilities Incurred |  | — |  |  | 49 |
Balance, December 31, 2017 |  | $ | 2,515 |  |  | $ | 1,945 |
(1) See Note 2, "Asset Sales and Impairments" for further discussion.

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