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Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Schedule of Equity Method Investments [Line Items] |  |  |  |
Equity income from unconsolidated investments, net | $ (17.4) | $ (12.7) | $ (30.8) | $ (23.6)
ATC Holdings [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Equity income from unconsolidated investments, net | (13.5) | (10.0) | (24.5) | (19.5)
Non-utility wind farm in Oklahoma [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Equity income from unconsolidated investments, net | (1.9) | (1.3) | (4.1) | (2.4)
Other [Member] |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |
Equity income from unconsolidated investments, net | $ (2.0) | $ (1.4) | $ (2.2) | $ (1.7)

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