Derivative Instruments (Details 4) (Not Designated as Hedging Instrument, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	$ (301)	[1]	$ (335)	[1]
Additions/Change in value of existing contracts	(344)	[1]	(207)	[1]
Settled contracts	247	[1]	241	[1]
Outstanding net asset (liability), Ending Balance	(398)	[1]	(301)	[1]
NUGs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(293)	[1]	(345)	[1]
Additions/Change in value of existing contracts	(201)		(202)	[1]
Settled contracts	240		254	[1]
Outstanding net asset (liability), Ending Balance	(254)	[1]	(293)	[1]
LCAPP
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	0	[1]	0	[1]
Additions/Change in value of existing contracts	(144)		0	[1]
Settled contracts	0		0	[1]
Outstanding net asset (liability), Ending Balance	(144)	[1]	0	[1]
Regulated FTRs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(8)	[1]	0	[1]
Additions/Change in value of existing contracts	1		(5)	[1]
Settled contracts	7		(3)	[1]
Outstanding net asset (liability), Ending Balance	0	[1]	(8)	[1]
Other
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	0	[1]	10	[1]
Additions/Change in value of existing contracts	0		0	[1]
Settled contracts	0		(10)	[1]
Outstanding net asset (liability), Ending Balance	$ 0	[1]	$ 0	[1]

[1] Changes in the fair value of certain contracts are deferred for future recovery from (or credited to) customers.