Segment and Related Information - Electric Utilities' Revenues (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Financial data for Products and Services
Electric Utilities Revenues	$ 16,478	$ 17,587	$ 17,374
Retail [Member]
Financial data for Products and Services
Electric Utilities Revenues	14,187	15,071	14,791
Wholesale [Member]
Financial data for Products and Services
Electric Utilities Revenues	1,675	1,905	1,994
Other Electric Revenue [Member]
Financial data for Products and Services
Electric Utilities Revenues	$ 616	$ 611	$ 589

Amount of revenue from external customers for the reportable segment. Such disclosure is presented if the amount is: (a) included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 131

-Paragraph 27

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration