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Equity Investments - Investment in Nobles 2 (Details) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 USD ($) MW | Mar. 31, 2020 USD ($) | Dec. 31, 2020 USD ($)
Investment in Nobles 2 [Line Items] |  |  |  |
Equity Investment Balance |  | $ 301.5 |  | $ 301.2
Cash Investments |  | 1.0 | $ 27.8 |
Equity Earnings |  | 4.8 | 5.2 |
Net Loss Attributable to Non-Controlling Interest |  | $ (8.4) | $ (1.8) |
Nobles 2 [Member] |  |  |  |
Investment in Nobles 2 [Line Items] |  |  |  |
Ownership Percentage |  | 49.00% |  |
Equity Investment Balance |  | $ 151.2 |  | 152.2
Cash Investments |  | 1.0 |  |
Distributed ATC Earnings |  | (1.5) |  |
Equity Earnings | [1] | (0.5) |  |
Net Loss Attributable to Non-Controlling Interest |  | $ 1.4 |  |
ATC [Member] |  |  |  |
Investment in Nobles 2 [Line Items] |  |  |  |
Ownership Percentage |  | 8.00% |  |
Equity Investment Balance |  | $ 150.3 |  | $ 149.0
Distributed ATC Earnings |  | (4.3) |  |
Equity Earnings |  | $ 5.3 |  |
Wind Turbine Generators [Member] | Tenaska [Member] | Minnesota Power [Member] | Tenaska PPA [Member] |  |  |  |
Investment in Nobles 2 [Line Items] |  |  |  |
Generating Capacity Counterparty Owned (MW) | MW |  | 250 |  |
Long-term Contract for Purchase of Electric Power, Term of Contract (Years) |  | 20 years |  |
[1] | The Company also recorded net loss attributable to non-controlling interest of $1.4 million related to its investment in Nobles 2.

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