Taxes (Details Textuals) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes (Textuals) [Abstract]
Effective income tax rate (percent)		35.30%	(24.60%)	34.20%
Change in accounting method		$ (8)	$ (27)	$ 0
Tax basis balance sheet adjustments	$ (16)		25
Pre-tax net operating loss carryforwards for state and local income tax purposes		10,000
Pre-tax net operating loss carryforwards expected to utilized		6,000
Unrecognized tax benefits	34	34	34	48	$ 43
Unrecognized tax benefits that would impact future tax rates		29
Unrecognized tax benefits, portion expected to be resolved in the next fiscal year		9
Unrecognized tax benefits that would impact effective tax rate		7
Reduction in effective tax rate		1	$ 6
Increase of accrued interest				$ 1
Federal
Income Taxes (Textuals) [Abstract]
Operating loss carryforwards, not subject to expiration		26
Operating loss carryforwards, subject to expiration		1,500
State and Local
Income Taxes (Textuals) [Abstract]
Operating loss carryforwards, subject to expiration		$ 398
FES
Income Taxes (Textuals) [Abstract]
Effective income tax rate (percent)		44.20%	38.80%	11.50%
Unrecognized tax benefits	$ 3	$ 8	$ 3	$ 3	$ 3