Derivative Instruments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	$ (438)	[1]	$ (445)	[1]	$ (301)	[1]	$ (335)	[1]
Additions/Change in value of existing contracts	(47)	[1]	(92)	[1]	(325)	[1]	(325)	[1]
Settled contracts	60	[1]	50	[1]	201	[1]	173	[1]
Outstanding net asset (liability), Ending Balance	(425)	[1]	(487)	[1]	(425)	[1]	(487)	[1]
NUGs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(293)	[1]	(447)	[1]	(293)	[1]	(345)	[1]
Additions/Change in value of existing contracts	(50)	[1]	(89)	[1]	(183)	[1]	(325)	[1]
Settled contracts	61	[1]	53	[1]	194	[1]	187	[1]
Outstanding net asset (liability), Ending Balance	(282)	[1]	(483)	[1]	(282)	[1]	(483)	[1]
LCAPP
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(145)	[1]	0	[1]	0	[1]	0	[1]
Additions/Change in value of existing contracts	3	[1]	0	[1]	(142)	[1]	0	[1]
Settled contracts	0	[1]	0	[1]	0	[1]	0	[1]
Outstanding net asset (liability), Ending Balance	(142)	[1]	0	[1]	(142)	[1]	0	[1]
Regulated FTRs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	0	[1]	2	[1]	(8)	[1]	0	[1]
Additions/Change in value of existing contracts	0	[1]	(3)	[1]	0	[1]	0	[1]
Settled contracts	(1)	[1]	(3)	[1]	7	[1]	(4)	[1]
Outstanding net asset (liability), Ending Balance	(1)	[1]	(4)	[1]	(1)	[1]	(4)	[1]
Other
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	0	[1]	0	[1]	0	[1]	10	[1]
Additions/Change in value of existing contracts	0	[1]	0	[1]	0	[1]	0	[1]
Settled contracts	0	[1]	0	[1]	0	[1]	(10)	[1]
Outstanding net asset (liability), Ending Balance	$ 0	[1]	$ 0	[1]	$ 0	[1]	$ 0	[1]

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