Financial Instruments, Derivatives, Guarantees and Concentration of Credit Risk (Details 2) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Fair value of energy commodity derivatives
Total derivatives, assets	$ 499	$ 573
Total derivatives, liabilities	176	289
Legacy natural gas contracts from former power business \| Not Designated as Hedging Instrument
Fair value of energy commodity derivatives
Total derivatives, assets	129	186
Total derivatives, liabilities	128	187
All other \| Not Designated as Hedging Instrument
Fair value of energy commodity derivatives
Total derivatives, assets	35	99
Total derivatives, liabilities	26	80
Designated as Hedging Instrument
Fair value of energy commodity derivatives
Total derivatives, assets	335	288
Total derivatives, liabilities	22	22
Not Designated as Hedging Instrument
Fair value of energy commodity derivatives
Total derivatives, assets	164	285
Total derivatives, liabilities	$ 154	$ 267

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624163-113959

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 44C

-Subparagraph a

-Clause 1

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 205G

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Name:	us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant