Related Party Transactions and Major Customers (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Related Party Transaction [Line Items]
Investments in Money Pool	$ 433	$ 1,000
Interest rate on money pool investment	0.10%
Notes receivable from parent	750	750
Note receivable prime interest rate	3.25%
Interest Income (Expense) Net, Related Party	19	19	19
Corporate service charges	143	142	132
Affiliates of NRG Energy, Inc. [Member]
Related Party Transaction [Line Items]
Sales to major customers	648	594	583
Affiliates of Energy Future Holdings Corp. [Member]
Related Party Transaction [Line Items]
Sales to major customers	$ 162	$ 182	$ 185