Taxes (Details Textuals) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes (Textuals) [Abstract]
Effective income tax rate (percent)		33.10%	35.30%	(24.60%)
Impairment	$ 800	$ 800
Impairment of non-deductible goodwill		433
Valuation allowances		246	$ 18	$ 33
Change in accounting method		0	(8)	(27)
Unrecognized tax benefits		84	$ 34	$ 34	$ 48
Unrecognized tax benefits that would impact future tax rates		50
Unrecognized tax benefits, portion expected to be resolved in the next fiscal year		51
Unrecognized tax benefits that would impact effective tax rate		26
Federal
Income Taxes (Textuals) [Abstract]
Operating loss carryforwards, not subject to expiration		25
Operating loss carryforwards, subject to expiration		1,800
State and Local
Income Taxes (Textuals) [Abstract]
Operating loss carryforwards valuation allowance		168
Operating loss carryforwards, subject to expiration		407
Pre-tax net operating loss carryforwards for state and local income tax purposes		10,100
Pre-tax net operating loss carryforwards expected to utilized		2,100
Operating loss carryforwards expected to utilized, net of tax		87
State and Local | Property [Member]
Income Taxes (Textuals) [Abstract]
Deferred tax assets valuation allowance		$ 78
FES
Income Taxes (Textuals) [Abstract]
Effective income tax rate (percent)		35.40%	44.20%	38.80%
Impairment	$ 23	$ 23
Valuation allowances		151	$ 14	$ 14
Unrecognized tax benefits		0	$ 8	$ 3	$ 3
FES | Federal
Income Taxes (Textuals) [Abstract]
Pre-tax net operating loss carryforwards for state and local income tax purposes		706
FES | State and Local
Income Taxes (Textuals) [Abstract]
Operating loss carryforwards valuation allowance		73
Operating loss carryforwards, subject to expiration		120
Pre-tax net operating loss carryforwards for state and local income tax purposes		3,400
FES | State and Local | Property [Member]
Income Taxes (Textuals) [Abstract]
Deferred tax assets valuation allowance		$ 78