Derivative Instruments (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	$ 0	$ 0	$ (129)
Not Designated as Hedging Instrument | Subject to Regulatory Accounting, Excluded from Earnings
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	(344)	(207)
Realized Gain (Loss) on Derivative Instrument	247	241
Not Designated as Hedging Instrument | Subject to Regulatory Accounting, Excluded from Earnings | NUGs
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	(201)	(202)
Realized Gain (Loss) on Derivative Instrument	240	254
Not Designated as Hedging Instrument | Subject to Regulatory Accounting, Excluded from Earnings | LCAPP
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	(144)	0
Realized Gain (Loss) on Derivative Instrument	0	0
Not Designated as Hedging Instrument | Subject to Regulatory Accounting, Excluded from Earnings | Regulated FTRs
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	1	(5)
Realized Gain (Loss) on Derivative Instrument	7	(3)
Not Designated as Hedging Instrument | Subject to Regulatory Accounting, Excluded from Earnings | Other
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	0	0
Realized Gain (Loss) on Derivative Instrument	$ 0	$ (10)