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Other Current Assets and Liabilities	9 Months Ended
Other Current Assets and Liabilities	Sep. 30, 2011
Other Current Assets and Liabilities [Abstract]
Other Current Assets and Liabilities	Other Current Assets and Liabilities Included in other current assets on the Condensed Consolidated Balance Sheets at December 31, 2010 and September 30, 2011 was $23 million and $14 million, respectively, of margin deposits and $99 million and $57 million, respectively, of under-recovered gas cost. Included in other current liabilities on the Condensed Consolidated Balance Sheets at December 31, 2010 and September 30, 2011 was $94 million and $20 million, respectively, of over-recovered gas cost.