Derivative Instruments (Details 4) (Not Designated as Hedging Instrument, Subject to Regulatory Accounting, Excluded from Earnings, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	$ 16	$ (80)
Realized Gain (Loss) on Derivative Instrument	22	76
NUGs
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	18	(79)
Realized Gain (Loss) on Derivative Instrument	23	72
LCAPP
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	(2)	0
Realized Gain (Loss) on Derivative Instrument	0	0
Regulated FTRs
Derivative [Line Items]
Unrealized Gain (Loss) on Derivative Instrument	0	(1)
Realized Gain (Loss) on Derivative Instrument	$ (1)	$ 4