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Pension and Other Postemployment Benefits (Details Textuals) - USD ($) $ in Millions |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 13, 2016 | Jan. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Mark-to-market adjustment, net of capitalized amounts |  |  | $ 141 | $ 147 | $ 242
Decrease in mortality rate (percent) |  |  | 0.50% |  |
Funding contributions made for current and future years |  |  |  | 882 |
Pension contributions | $ 500 |  | $ 0 | 382 | 143
Equity contribution from parent |  |  |  | 500 |
Non-cash transaction: stock contribution to pension plan |  |  | 0 | 500 | 0
Pensions and OPEB |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual return on plan assets |  |  | $ 999 | $ 472 | $ (172)
Actual return on plan assets (percent) |  |  | 15.10% | 8.20% | (2.70%)
Expected return on plan assets |  |  | $ 478 | $ 429 | $ 476
Pension |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Company contributions |  |  | 18 | 899 |
Actual return on plan assets |  |  | $ 950 | $ 442 |
Expected long-term return on plan assets |  |  | 7.50% | 7.50% | 7.75%
Expected return on plan assets |  |  | $ 448 | $ 399 | $ 443
Increase in benefit obligation due to RP2014 mortality table |  |  | 62 |  |
Excluded from total investments |  |  | (10) | 16 |
OPEB |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Company contributions |  |  | 16 | 9 |
Actual return on plan assets |  |  | $ 49 | $ 30 |
Expected long-term return on plan assets |  |  | 7.50% | 7.50% | 7.75%
Expected return on plan assets |  |  | $ 30 | $ 30 | $ 33
Excluded from total investments |  |  | (2) | (4) |
Minimum |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Company contributions |  |  |  | 382 |
FE | Pension |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Non-cash transaction: stock contribution to pension plan |  |  |  | 293 |
FES |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Pension contributions |  |  | $ 0 | $ 138 | $ 0
Subsequent Event |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Funding contributions made for current and future years |  | $ 750 |  |  |
Subsequent Event | Minimum |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Company contributions |  | $ 500 |  |  |

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