Discontinued Operations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 MW
Maine Hydro [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capacity associated with discontinued operations (in megawatts)	351
Assumption of debt	$ 700
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	372
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	231
Maine fossil [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capacity associated with discontinued operations (in megawatts)	796
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	(67)
Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax	$ (43)