Derivative Instruments And Hedging Activities (Derivative Gain (Loss) Amounts Recognized In Income) (Details) (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Realized mark-to-market gains (losses)	$ 1	$ 1	$ (1)	$ 2
Unrealized mark-to-market gains (losses)	(5)		(10)
Total net mark-to-market gains (losses)	(4)	1	(11)	2
Revenue [Member]
Realized mark-to-market gains (losses)	1	1	(1)	2
Unrealized mark-to-market gains (losses)	(5)		(10)
Total net mark-to-market gains (losses)	(4)	1	(11)	2
Fuel And Purchased Energy Expense [Member]
Realized mark-to-market gains (losses)
Unrealized mark-to-market gains (losses)
Total net mark-to-market gains (losses)

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585

Name:	us-gaap_UnrealizedGainLossOnDerivatives
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration