Derivative Instruments (Details 4) (Not Designated as Hedging Instrument, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	$ (202)	$ (398)
Unrealized gain (loss)	(12)	41
Additions	11	(3)
Terminations		166
Settlements	39	74
Outstanding net asset (liability), Ending Balance	(140)	(202)
NUGs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(202)	(254)
Unrealized gain (loss)	1	23
Additions	0	0
Terminations		0
Settlements	52	75
Outstanding net asset (liability), Ending Balance	(151)	(202)
LCAPP
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	0	(144)
Unrealized gain (loss)	0	22
Additions	0	0
Terminations		166
Settlements	0	0
Outstanding net asset (liability), Ending Balance	0	0
Regulated FTRs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	0	0
Unrealized gain (loss)	(13)	(4)
Additions	11	(3)
Terminations		0
Settlements	(13)	(1)
Outstanding net asset (liability), Ending Balance	$ 11	$ 0