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Equity Investments - Investment in Nobles 2 (Details) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2021 USD ($) MW | Jun. 30, 2020 USD ($) | Jun. 30, 2021 USD ($) MW | Jun. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Investment in Nobles 2 [Line Items] |  |  |  |  |  |
Equity Investment Balance |  | $ 317.8 |  | $ 317.8 |  | $ 301.2
Cash Investments |  |  |  | 17.1 | $ 66.6 |
Equity Earnings |  | 5.1 | $ 6.4 | 9.9 | 11.6 |
Net Loss Attributable to Non-Controlling Interest |  | $ (6.2) | $ (3.2) | $ (14.6) | $ (5.0) |
Nobles 2 [Member] |  |  |  |  |  |
Investment in Nobles 2 [Line Items] |  |  |  |  |  |
Ownership Percentage |  | 49.00% |  | 49.00% |  |
Equity Investment Balance |  | $ 166.2 |  | $ 166.2 |  | 152.2
Cash Investments |  |  |  | 17.1 |  |
Distributed Earnings |  |  |  | (2.5) |  |
Equity Earnings | [1] |  |  | (0.6) |  |
Net Loss Attributable to Non-Controlling Interest |  |  |  | $ 3.4 |  |
ATC [Member] |  |  |  |  |  |
Investment in Nobles 2 [Line Items] |  |  |  |  |  |
Ownership Percentage |  | 8.00% |  | 8.00% |  |
Equity Investment Balance |  | $ 151.6 |  | $ 151.6 |  | $ 149.0
Distributed Earnings |  |  |  | (8.5) |  |
Equity Earnings |  |  |  | $ 10.5 |  |
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 |  | 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 $3.4 million related to its investment in Nobles 2.

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