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Other Current Assets and Liabilities	6 Months Ended
Other Current Assets and Liabilities	Jun. 30, 2011
Other Current Assets and Liabilities [Abstract]
Other Current Assets and Liabilities	(14) Other Current Assets and Liabilities Included in other current assets on the Condensed Consolidated Balance Sheets at December 31, 2010 and June 30, 2011 was $23 million and $18 million, respectively, of margin deposits and $99 million and $66 million, respectively, of under-recovered gas cost. Included in other current liabilities on the Condensed Consolidated Balance Sheets at December 31, 2010 and June 30, 2011 was $94 million and $48 million, respectively, of over-recovered gas cost.