Derivative Instruments (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	$ (305)	[1]	$ (362)	[1]	$ (301)	[1]	$ (335)	[1]
Additions/Change in value of existing contracts	(199)	[1]	(145)	[1]	(279)	[1]	(234)	[1]
Settled contracts	66	[1]	62	[1]	142	[1]	124	[1]
Outstanding net asset (liability), Ending Balance	(438)	[1]	(445)	[1]	(438)	[1]	(445)	[1]
NUGs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(300)	[1]	(362)	[1]	(293)	[1]	(345)	[1]
Additions/Change in value of existing contracts	(54)	[1]	(147)	[1]	(133)	[1]	(236)	[1]
Settled contracts	61	[1]	62	[1]	133	[1]	134	[1]
Outstanding net asset (liability), Ending Balance	(293)	[1]	(447)	[1]	(293)	[1]	(447)	[1]
LCAPP
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	0	[1]	0	[1]	0	[1]	0	[1]
Additions/Change in value of existing contracts	(145)	[1]	0	[1]	(145)	[1]	0	[1]
Settled contracts	0	[1]	0	[1]	0	[1]	0	[1]
Outstanding net asset (liability), Ending Balance	(145)	[1]	0	[1]	(145)	[1]	0	[1]
Regulated FTRs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(5)	[1]	0	[1]	(8)	[1]	0	[1]
Additions/Change in value of existing contracts	0	[1]	2	[1]	(1)	[1]	2	[1]
Settled contracts	5	[1]	0	[1]	9	[1]	0	[1]
Outstanding net asset (liability), Ending Balance	0	[1]	2	[1]	0	[1]	2	[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.