Derivative Instruments (Details Textuals) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) agreement	Dec. 31, 2016 USD ($) agreement
Derivative [Line Items]
Gains included in long-term debt associated with prior fixed-for-floating interest rate swap agreements	$ 3	$ 10
Expected adverse change in quoted market prices of derivative instruments	10.00%
Decrease net income due to adverse change in commodity prices	$ 6
NUGs
Derivative [Line Items]
Liability position	79
Cash Flow Hedges
Derivative [Line Items]
Unamortized gains or (losses) associated with designated cash flow hedges	(10)	(12)
Unamortized losses associated with prior interest rate hedges	$ 25	$ 33
Number of forward starting swap agreements accounted for as a cash flow hedge outstanding | agreement	0	0
Fair Value Hedging
Derivative [Line Items]
Gains (losses) to be amortized to interest expenses during next twelve months	$ (2)
Reclassifications from long-term debt	$ 7	$ 10
Number of fixed-for-floating interest rate swap agreements outstanding | agreement	0	0
FES
Derivative [Line Items]
Decrease net income due to adverse change in commodity prices	$ 4
FES | Commodity contracts
Derivative [Line Items]
Collateral posted	1
FES | Cash Flow Hedges
Derivative [Line Items]
Unamortized losses associated with prior interest rate hedges	$ 3	$ 3