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Investments (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended | 9 Months Ended
--- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Jun. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Schedule of Investments [Line Items] |  |  |  |  |
Equity (income) loss from unconsolidated investments, net | $ (9.8) | $ (10.1) |  | $ (41.6) | $ (32.9)
Non-utility wind farm In Oklahoma [Member] |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Equity (income) loss from unconsolidated investments, net | $ 0.1 | $ 0.2 | $ 0.0 | $ (14.5) | $ 0.2

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