Derivative Instruments (Details Textuals) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) agreement	Dec. 31, 2015 USD ($) agreement
Derivative [Line Items]
Gains included in long-term debt associated with prior fixed-for-floating interest rate swap agreements	$ 10	$ 20
Expected adverse change in quoted market prices of derivative instruments	10.00%
Decrease net income due to adverse change in commodity prices	$ 29
NUGs
Derivative [Line Items]
Liability position	107
FTRs
Derivative [Line Items]
Net asset position under commodity derivative contracts	1
Collateral posted	1
Cash Flow Hedges
Derivative [Line Items]
Unamortized gains or (losses) associated with designated cash flow hedges	(12)	(11)
Unamortized gains or (losses) associated with prior interest rate hedges	(33)	$ (42)
Gains (losses) to be amortized to interest expenses during next twelve months	$ (8)
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	$ (7)
Reclassifications from long-term debt	$ 10	$ 12
Number of fixed-for-floating interest rate swap agreements outstanding | agreement	0	0
Interest rate swaps
Derivative [Line Items]
Number of interest rate swaps outstanding | agreement	0	0
FES | Commodity contracts
Derivative [Line Items]
Net asset position under commodity derivative contracts	$ 86
Collateral posted	52
FES | FTRs
Derivative [Line Items]
Collateral posted	5
FES | Cash Flow Hedges
Derivative [Line Items]
Unamortized gains or (losses) associated with prior interest rate hedges	$ (3)	$ (3)