Fair Value Measurements (Quantitative Information About Level 3 Fair Value Measurements) (Details) (USD $) In Millions, unless otherwise specified						6 Months Ended		6 Months Ended
Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Level 3	Dec. 31, 2011 Level 3	Jun. 30, 2012 Level 3 Electricity Congestion Contracts	Jun. 30, 2012 Level 3 Electricity Congestion Contracts Latest Auction Pricing Congestion Prices Minimum	Jun. 30, 2012 Level 3 Electricity Congestion Contracts Latest Auction Pricing Congestion Prices Maximum	Jun. 30, 2012 Level 3 Electricity Congestion Contracts Latest Auction Pricing Congestion Prices Weighted Average	Jun. 30, 2012 Level 3 Electricty Power Contracts	Jun. 30, 2012 Level 3 Electricty Power Contracts Discounted Cash Flow Power Prices Minimum	Jun. 30, 2012 Level 3 Electricty Power Contracts Discounted Cash Flow Power Prices Maximum	Jun. 30, 2012 Level 3 Electricty Power Contracts Discounted Cash Flow Power Prices Weighted Average	Jun. 30, 2012 Level 3 Netting
Quantitative Information About Level 3 Measurements [Line Items]
Fair Value, Assets	$ 971	$ 1,306	$ 51	$ 95	$ 73				$ 19				$ (41)
Fair Value, Liabilities	$ 114	$ 91	$ 10	$ 12	$ 24				$ 27				$ (41)
Expected prices (in dollars per unit)						(15.52)	23.03	0.15		16.60	58.23	35.80

This element represents the aggregate of the liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Name:	us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant