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Pension and Other Postemployment Benefits (Details 10) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Pension |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Net Periodic Cost (Credit) | $ 265 | $ 377 | $ 485
Pension | FES |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Net Periodic Cost (Credit) | 60 | (5) | 10
OPEB |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Net Periodic Cost (Credit) | (66) | (60) | (108)
OPEB | FES |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |  |
Net Periodic Cost (Credit) | $ (17) | $ (26) | $ (22)

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- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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