Variable Interest Entities, or VIEs (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Investments Accounted for by the Equity Method
Equity investments in affiliates	$ 643	$ 640
Gen Conn Energy LLC [Member]
Investments Accounted for by the Equity Method
Economic interest in equity method investments (as a percent)	50.00%
Power generation units	2
Generation capacity (in MW)	200
Equity investments in affiliates	131
Texas Coastal Ventures, LLC [Member]
Investments Accounted for by the Equity Method
Economic interest in equity method investments (as a percent)	50.00%
Equity investments in affiliates	49
Sherbino I Wind Farm LLC [Member]
Investments Accounted for by the Equity Method
Economic interest in equity method investments (as a percent)	50.00%
Equity investments in affiliates	$ 98