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Investment in Transmission Affiliates - ATC Return on Equity (Details) - ATC $ in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended
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Oct. 31, 2024 | Aug. 31, 2022 | Dec. 31, 2024 USD ($) numberOfComplaints | Sep. 30, 2022 USD ($) | Dec. 31, 2024 USD ($) numberOfComplaints | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Allowed return on equity for American Transmission Company LLC |  |  |  |  |  |  |
Number of complaints filed | numberOfComplaints |  |  | 2 |  | 2 |  |
Earnings (loss) from equity method investment |  |  |  |  | $ 205.4 | $ 175.1 | $ 192.6
Opinion issued by United States Court of Appeals for the District of Columbia Circuit in August 2022 |  |  |  |  |  |  |
Allowed return on equity for American Transmission Company LLC |  |  |  |  |  |  |
Assumed return on equity (as a percent) |  | 9.88% |  |  |  |  |
Earnings (loss) from equity method investment |  |  |  | $ 39.1 |  |  |
Order issued by the Federal Energy Regulatory Commission in October 2024 |  |  |  |  |  |  |
Allowed return on equity for American Transmission Company LLC |  |  |  |  |  |  |
Approved return on equity (as a percent) | 9.98% |  |  |  |  |  |
Earnings (loss) from equity method investment |  |  | $ 20.1 |  |  |  |

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