Fair Value Measurements (Details 1) - Level 3 - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
NUG contracts
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	$ 2	$ 20
Beginning Balance, Derivative Liabilities	(153)	(222)
Beginning Balance, Net	(151)	(202)
Unrealized gain (loss), Derivative Assets	1	2
Unrealized gain (loss), Derivative Liabilities	(17)	(2)
Unrealized gain (loss), Net	(16)	0
Purchases, Derivative Assets	0	0
Purchases, Derivative Liabilities	0	0
Purchases, Net	0	0
Settlements, Derivative Assets	(2)	(20)
Settlements, Derivative Liabilities	29	71
Settlements, Net	27	51
Ending Balance, Derivative Assets	1	2
Ending Balance, Derivative Liabilities	(141)	(153)
Ending Balance, Net	(140)	(151)
FTRs
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	39	4
Beginning Balance, Derivative Liabilities	(14)	(12)
Beginning Balance, Net	25	(8)
Unrealized gain (loss), Derivative Assets	5	47
Unrealized gain (loss), Derivative Liabilities	3	(1)
Unrealized gain (loss), Net	8	46
Purchases, Derivative Assets	22	26
Purchases, Derivative Liabilities	(11)	(16)
Purchases, Net	11	10
Settlements, Derivative Assets	(43)	(38)
Settlements, Derivative Liabilities	9	15
Settlements, Net	(34)	(23)
Ending Balance, Derivative Assets	23	39
Ending Balance, Derivative Liabilities	(13)	(14)
Ending Balance, Net	10	25
FTRs | FES
Reconciliation of changes in the fair value of NUG contracts
Beginning Balance, Derivative Assets	27	3
Beginning Balance, Derivative Liabilities	(13)	(11)
Beginning Balance, Net	14	(8)
Unrealized gain (loss), Derivative Assets	4	34
Unrealized gain (loss), Derivative Liabilities	3	(1)
Unrealized gain (loss), Net	7	33
Purchases, Derivative Assets	9	15
Purchases, Derivative Liabilities	(10)	(16)
Purchases, Net	(1)	(1)
Settlements, Derivative Assets	(30)	(25)
Settlements, Derivative Liabilities	9	15
Settlements, Net	(21)	(10)
Ending Balance, Derivative Assets	10	27
Ending Balance, Derivative Liabilities	(11)	(13)
Ending Balance, Net	$ (1)	$ 14