Asset Impairment Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2012	Sep. 30, 2012	Sep. 30, 2011
Asset Impairment Expense [Line Items]
Asset Impairment Charges	$ 43	$ 130		$ 72	$ 163
Wind turbines and projects [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges	36	116		40	116
Wind Turbines [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges		116		20
Fair Value	25			25
Carrying Amount	45			45
Wind projects [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges				16
St Patrick [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges	0	0	11	11	0
Fair Value			22
Carrying Amount			33
Kelanitissa [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges	5	4		17	37
Fair Value	10			10
Carrying Amount	22			22
Other Impairment [Member]
Asset Impairment Expense [Line Items]
Asset Impairment Charges	$ 2	$ 10		$ 4	$ 10