Fair Value Measurements (Details 1) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
NUG contracts
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	$ 1	$ 2
Beginning Balance, Derivative Liabilities	(137)	(153)
Beginning Balance, Net	(136)	(151)
Unrealized gain (loss), Derivative Assets	2	2
Unrealized gain (loss), Derivative Liabilities	(17)	(49)
Unrealized gain (loss), Net	(15)	(47)
Purchases, Derivative Assets	0	0
Purchases, Derivative Liabilities	0	0
Purchases, Net	0	0
Settlements, Derivative Assets	(2)	(3)
Settlements, Derivative Liabilities	46	65
Settlements, Net	44	62
Ending Balance, Derivative Assets	1	1
Ending Balance, Derivative Liabilities	(108)	(137)
Ending Balance, Net	(107)	(136)
FTRs
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	8	39
Beginning Balance, Derivative Liabilities	(13)	(14)
Beginning Balance, Net	(5)	25
Unrealized gain (loss), Derivative Assets	(6)	(5)
Unrealized gain (loss), Derivative Liabilities	(4)	(7)
Unrealized gain (loss), Net	(10)	(12)
Purchases, Derivative Assets	16	22
Purchases, Derivative Liabilities	(7)	(11)
Purchases, Net	9	11
Settlements, Derivative Assets	(11)	(48)
Settlements, Derivative Liabilities	18	19
Settlements, Net	7	(29)
Ending Balance, Derivative Assets	7	8
Ending Balance, Derivative Liabilities	(6)	(13)
Ending Balance, Net	1	(5)
FES | FTRs
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	5	27
Beginning Balance, Derivative Liabilities	(11)	(13)
Beginning Balance, Net	(6)	14
Unrealized gain (loss), Derivative Assets	(4)	2
Unrealized gain (loss), Derivative Liabilities	(3)	(5)
Unrealized gain (loss), Net	(7)	(3)
Purchases, Derivative Assets	10	9
Purchases, Derivative Liabilities	(5)	(10)
Purchases, Net	5	(1)
Settlements, Derivative Assets	(7)	(33)
Settlements, Derivative Liabilities	14	17
Settlements, Net	7	(16)
Ending Balance, Derivative Assets	4	5
Ending Balance, Derivative Liabilities	(5)	(11)
Ending Balance, Net	$ (1)	$ (6)