Derivative Instruments (Details Textuals) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) agreement	Dec. 31, 2017 USD ($) agreement
Derivative [Line Items]
Unamortized gains included in long term debt associated with prior fixed for floating interest rate swap agreements	$ 2	$ 3
NUGs
Derivative [Line Items]
Net liability position	44	79
Settlements	33
Unrealized gain (loss)	2
FTRs
Derivative [Line Items]
Settlements	3
Unrealized gain (loss)	9
Net asset position	9	3
Cash Flow Hedges
Derivative [Line Items]
Unamortized losses associated with prior interest rate hedges	15	$ 22
Gains (losses) to be amortized to interest expenses during next twelve months	$ (2)
Number of forward starting swap agreements accounted for as a cash flow hedge outstanding | agreement	0	0
Fair Value Hedging
Derivative [Line Items]
Number of fixed-for-floating interest rate swap agreements outstanding | agreement	0	0