Derivative Instruments (Details 5) (Not Designated as Hedging Instrument, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	$ (398)	[1]	$ (301)	[1]
Additions/Change in value of existing contracts	16	[1]	(80)	[1]
Settled contracts	22	[1]	76	[1]
Outstanding net asset (liability), Ending Balance	(360)	[1]	(305)	[1]
NUGs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(254)	[1]	(293)	[1]
Additions/Change in value of existing contracts	18	[1]	(79)	[1]
Settled contracts	23	[1]	72	[1]
Outstanding net asset (liability), Ending Balance	(213)	[1]	(300)	[1]
LCAPP
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	(144)	[1]	0	[1]
Additions/Change in value of existing contracts	(2)	[1]	0	[1]
Settled contracts	0	[1]	0	[1]
Outstanding net asset (liability), Ending Balance	(146)	[1]	0	[1]
Regulated FTRs
Outstanding net asset (liability) [Roll Forward]
Outstanding net asset (liability), Beginning Balance	0	[1]	(8)	[1]
Additions/Change in value of existing contracts	0	[1]	(1)	[1]
Settled contracts	(1)	[1]	4	[1]
Outstanding net asset (liability), Ending Balance	$ (1)	[1]	$ (5)	[1]

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