v3.3.0.814

Acquisition (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($)	Dec. 31, 2015 MWh	Oct. 12, 2015 USD ($) MW	Oct. 01, 2015 USD ($)	Dec. 31, 2014 USD ($) MW
Fore River Energy Center [Member]
Business Acquisition [Line Items]
Business combination, recognized identifiable assets acquired and liabilities assumed, net					$ 530
Power generation capacity | MW					731
Osprey Energy Center [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Productive Assets	$ 166
Osprey Energy Center Agreement Term	27 months
Subsequent event [Member] | Granite Ridge Energy Center [Member]
Business Acquisition [Line Items]
Business combination, recognized identifiable assets acquired and liabilities assumed, net			$ 500
Power generation capacity | MW			745
Subsequent event [Member] | Crane Champion Holdco, LLC [Member]
Business Acquisition [Line Items]
Ownership percentage of acquiree				75.00%
Subsequent event [Member] | EDF Trading North America, LLC [Member]
Business Acquisition [Line Items]
Ownership percentage of acquiree				25.00%
Subsequent event [Member] | Champion Energy Marketing, LLC [Member]
Business Acquisition [Line Items]
Business combination, recognized identifiable assets acquired and liabilities assumed, net				$ 240
Electricity sales volume | MWh		22,000,000

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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-Name Accounting Standards Codification



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