v3.8.0.1

Acquisition (Details) $ in Millions | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2017 USD ($) | Sep. 30, 2017 USD ($) | Jan. 17, 2017 USD ($) | Feb. 05, 2016 USD ($) MW
North American Power [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Ownership percentage of acquiree |  |  | 100.00% |
Business combination, recognized identifiable assets acquired and liabilities assumed, net |  |  | $ 105 |
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
Summer Peaking Capacity | MW |  |  |  | 695
Osprey Energy Center [Member] |  |  |  |
Business Acquisition [Line Items] |  |  |  |
Proceeds from Sale of Productive Assets | $ 166 |  |  |
Gain (Loss) on Sale of Assets and Asset Impairment Charges |  | $ 27 |  |

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