Asset Impairment Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 MWh	Mar. 31, 2012
Asset Impairment Expense [Line Items]
Asset Impairment Charges	$ 48	$ 10
Generation Capacity (MW)	125
Beaver Valley [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges	46	0
Lump Sum Payment Received For Termination Of PPA	60
Kelanitissa [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges	0	5
Other Impairment [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges	$ 2	$ 5