Discontinued Operations (Details) (Maine Hydro [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 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

Capacity associated with discontinued operations (in megawatts)

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- Definition

Amount of gain (loss), before tax expense or benefit and not previously recognized, resulting from the sale of a business component.

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Amount of gain (loss), after tax expense or benefit and not previously recognized, resulting from the sale of a business component.

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- Definition

The fair value of liabilities assumed in noncash investing or financing activities.

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