Pension and Other Postemployment Benefits (Details 10) - USD ($) $ in Millions	12 Months Ended
	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)