Taxes (Details Textuals) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes (Textuals) [Abstract]
Valuation allowances		$ 21	$ 11	$ 160
Effective income tax rate (percent)		32.40%	120.30%	49.00%
Effective income tax rate excluding effect of deferred taxes, (percent)			43.30%
Unrecognized tax benefits		$ 158	$ 80	$ 84	$ 26
Increase resulting from nondeductible interest		27
Increase in worthless stock deduction reserve		88
Unrecognized tax benefits that would impact future tax rates		142
Decrease in unrecognized tax benefits is reasonably possible	$ 45
Unrecognized tax benefits, portion expected to be resolved in the next fiscal year		6
Unrecognized tax benefits that would impact effective tax rate		2
Federal
Income Taxes (Textuals) [Abstract]
Operating loss carryforwards, not subject to expiration		18
Federal | Begin To Expire in 2031
Income Taxes (Textuals) [Abstract]
Pre-tax net operating loss carryforwards		2,400
Operating loss carryforwards, subject to expiration		493
State and Local
Income Taxes (Textuals) [Abstract]
Pre-tax net operating loss carryforwards		7,600
Operating loss carryforwards, subject to expiration		365
Pre-tax net operating loss carryforwards expected to utilized		2,000
Operating loss carryforwards expected to utilized, net of tax		100
Tax deferred expense, net of tax		59
West Virginia | State and Local
Income Taxes (Textuals) [Abstract]
Valuation allowances	$ 126
FES and FENOC | Discontinued Operations, Disposed of by Means Other than Sale
Income Taxes (Textuals) [Abstract]
Valuation allowances		60
Nondeductible portion of interest expense		$ 60	$ 27