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Pension and Other Post-Employment Benefits (Details) - USD ($) $ in Millions |  | 3 Months Ended
--- | --- | ---
Feb. 01, 2019 | Mar. 31, 2020 | Mar. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Net periodic costs (credits), including amounts capitalized |  | $ 246 |
Mark-to-market adjustment |  | $ 423 |
Decrease in discount rate |  | 0.38% |
Contributions by employer | $ 500 |  |
Pension |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Service costs |  | $ 52 | $ 48
Interest costs |  | 75 | 93
Expected return on plan assets |  | (153) | (135)
Amortization of prior service costs (credits) |  | 10 | 2
Special termination costs |  | 0 | 15
One-time termination benefit |  | 8 | 0
Pension and OPEB mark-to-market adjustment |  | 386 | 0
Net periodic costs (credits), including amounts capitalized |  | 378 | 23
Net periodic costs (credits), recognized in earnings |  | 358 | 6
Net accelerated credits |  | $ 18 |
Discount rate |  | 2.96% |
OPEB |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Service costs |  | $ 1 | 1
Interest costs |  | 4 | 5
Expected return on plan assets |  | (8) | (7)
Amortization of prior service costs (credits) |  | (33) | (9)
Special termination costs |  | 0 | 0
One-time termination benefit |  | 0 | 0
Pension and OPEB mark-to-market adjustment |  | 37 | 0
Net periodic costs (credits), including amounts capitalized |  | 1 | (10)
Net periodic costs (credits), recognized in earnings |  | $ 1 | (10)
Discount rate |  | 2.80% |
Estimated return |  | 7.50% |
FES | Affiliated Companies | Benefit Obligations | FES and FENOC | Discontinued Operations, Disposed of by Means Other than Sale |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Amounts of transaction |  | $ 6 | $ 10

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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