Taxes (Details 1) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of federal income tax expense at the federal statutory rate to the total provision for income taxes
Income from Continuing Operations before income taxes									$ 893	$ 171	$ 570
Federal income tax expense at statutory rate (35%)									313	60	199
Increases (reductions) in taxes resulting from-
State income taxes, net of federal tax benefit									34	12	10
AFUDC equity and other flow-through									(16)	(13)	(7)
Amortization of investment tax credits									(8)	(10)	(8)
Change in accounting method									(8)	(27)	0
ESOP dividend									(6)	(6)	(9)
Tax basis balance sheet adjustments									0	(25)	0
Uncertain tax positions									1	(35)	(2)
Other, net									5	2	12
Total provision for income taxes	$ (170)	$ 226	$ 115	$ 144	$ (268)	$ 152	$ 26	$ 48	$ 315	$ (42)	$ 195
Effective income tax rate (percent)									35.30%	(24.60%)	34.20%
FES
Reconciliation of federal income tax expense at the federal statutory rate to the total provision for income taxes
Income from Continuing Operations before income taxes									$ 147	$ (588)	$ 52
Federal income tax expense at statutory rate (35%)									51	(206)	18
Increases (reductions) in taxes resulting from-
State income taxes, net of federal tax benefit									16	(14)	(5)
Amortization of investment tax credits									(2)	(4)	(4)
ESOP dividend									(1)	(1)	(2)
Uncertain tax positions									5	0	0
Other, net									(4)	(3)	(1)
Total provision for income taxes	$ 1	$ 70	$ (4)	$ (2)	$ (133)	$ 28	$ (67)	$ (56)	$ 65	$ (228)	$ 6
Effective income tax rate (percent)									44.20%	38.80%	11.50%