Property, Plant And Equipment (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 mW	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Decommissioning costs	$ 2	$ 4
Generating Capacity	790
Subsidiaries [Member]
Property, Plant and Equipment [Line Items]
Jointly owned plant, net book value ownership	$ 13	$ 14