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Pension and Other Postemployment Benefits - Narrative (Details) - USD ($) $ in Millions |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | ---
Feb. 01, 2019 | Jan. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Mark-to-market adjustment, net of capitalized amounts |  |  | $ 676 | $ 145 | $ 141
Increase in discount rate |  |  | 1.10% |  |
Company contributions | $ 500 |  |  |  |
Funding contributions made for current and future years |  | $ 750 |  |  |
Pensions and OPEB |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual return on plan assets |  |  | $ 1,492 | $ 371 | $ 999
Actual return on plan assets (percent) |  |  | 20.20% | (4.00%) | 15.10%
Expected return on plan assets |  |  | $ 569 | $ 605 | $ 478
Pension |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Company contributions |  |  | 521 | 1,270 |
Actual return on plan assets |  |  | $ 1,419 | $ (363) |
Expected long-term return on plan assets |  |  | 7.50% | 7.50% | 7.50%
Expected return on plan assets |  |  | $ 540 | $ 574 | $ 448
Increase in benefit obligation due to RP2014 mortality table |  |  | 29 |  |
Net periodic benefit costs (credits) |  |  | 703 | 287 | $ 265
Excluded from total investments |  |  | 176 | 68 |
OPEB |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Company contributions |  |  | 21 | 22 |
Actual return on plan assets |  |  | $ 73 | $ (8) |
Expected long-term return on plan assets |  |  | 7.50% | 7.50% | 7.50%
Expected return on plan assets |  |  | $ 29 | $ 31 | $ 30
Increase in benefit obligation due to RP2014 mortality table |  |  | 3 |  |
Net periodic benefit costs (credits) |  |  | (20) | (156) | (66)
Excluded from total investments |  |  | 1 | (2) |
Minimum |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Company contributions |  | $ 500 |  |  |
Discontinued Operations |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Mark-to-market adjustment, net of capitalized amounts |  |  | 2 | 1 | 39
FES and FENOC | Discontinued Operations, Disposed of by Means Other than Sale |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Expenses from transactions with related parties |  |  | 37 | 42 |
FES and FENOC | Discontinued Operations, Disposed of by Means Other than Sale | Pension |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Net periodic benefit costs (credits) |  |  | 242 | 64 | 60
FES and FENOC | Discontinued Operations, Disposed of by Means Other than Sale | OPEB |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Net periodic benefit costs (credits) |  |  | $ (19) | $ (25) | $ (17)

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