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Pension and Other Postemployment Benefits (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Dec. 31, 2016
Pension |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Service costs | $ 52 | $ 48 | $ 104 | $ 96 |
Interest costs | 97 | 99 | 194 | 199 |
Expected return on plan assets | (112) | (100) | (224) | (197) |
Amortization of prior service costs (credits) | 2 | 2 | 4 | 4 |
Net periodic costs (credits) | 39 | 49 | 78 | 102 |
OPEB |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Service costs | 1 | 1 | 2 | 2 |
Interest costs | 7 | 8 | 14 | 15 |
Expected return on plan assets | (7) | (8) | (15) | (16) |
Amortization of prior service costs (credits) | (20) | (20) | (40) | (40) |
Net periodic costs (credits) | (19) | (19) | (39) | (39) |
FirstEnergy | Pension |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Net periodic benefit expense (credit) | 27 | 35 | 59 | 72 |
FirstEnergy | OPEB |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Net periodic benefit expense (credit) | (14) | (15) | (29) | (30) |
FES |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Non-current liabilities | 866 |  | 866 |  | $ 866
FES | Pension |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Net periodic costs (credits) | 3 | 6 | 6 | 12 |
Net periodic benefit expense (credit) | 3 | 6 | 6 | 12 |
FES | OPEB |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Net periodic costs (credits) | (4) | (4) | (8) | (8) |
Net periodic benefit expense (credit) | (4) | $ (4) | (8) | $ (8) |
FENOC |  |  |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |  |  |
Non-current liabilities | $ 570 |  | $ 570 |  | $ 570

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- Definition Amount of liability, recognized in statement of financial position, for defined benefit pension plan, classified as noncurrent. Excludes other postretirement benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(24)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1731-114919 + Details
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