Derivative Instruments And Hedging Activities (Cash Flow Hedges Related To Effective Portion Of Gain Or Loss On Derivatives) (Details) (USD $) In Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010		Jun. 30, 2011	Jun. 30, 2010
Derivative Instruments And Hedging Activities
Amount of net pre-tax loss arising during the period included in accumulated other comprehensive loss	$ 3	$ 12		$ 2	$ (78)
Effective portion of Fuel and Purchased Energy	19	39		46	85
Ineffective portion of Revenue		(1)	[1],[2]		2	[1],[2]
Total net pre-tax loss reclassified into income	19	38		46	87
Net pre-tax gain (loss) on commodity derivatives included in accumulated other comprehensive loss	22	50		48	9
Derivative gain loss reclassified from AOCL to income	$ 0	$ 1		$ 0	$ 1

[1] For the six months ended June 30, 2011 and 2010, amounts of zero and less than $1 million, respectively, were reclassified from AOCL to income because the forecasted hedged transactions were deemed probable not to occur.

[2] For the three months ended June 30, 2011 and 2010, amounts of zero and less than $1 million, respectively, were reclassified from AOCL to income because the forecasted hedged transactions were deemed probable not to occur.