Related Party Transactions and Major Customers (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Related Party Transaction [Line Items]
Investments in Money Pool	$ 177		$ 433
Notes Receivable from Parent	750		750
Interest Income (Expense) Net, Related Party	5	5
Corporate service charges	36	37
Affiliates of NRG Energy, Inc. [Member]
Related Party Transaction [Line Items]
Sales to major customers	144	140
Affiliates of Energy Future Holdings Corp. [Member]
Related Party Transaction [Line Items]
Sales to major customers	$ 36	$ 36

For an unclassified balance sheet, amounts due from parties associated with the reporting entity as evidenced by a written promise to pay.

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

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

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

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Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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+ Details