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INVESTMENT IN TRANSMISSION AFFILIATES - CHANGES TO INVESTMENTS (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022
Changes to investments in transmission affiliates |  |  |  |
Add: Earnings from equity method investment | $ 43.6 | $ 43.0 | $ 87.4 | $ 84.7
Add: Capital contributions |  |  | 33.3 | 30.3
Transmission Affiliates |  |  |  |
Changes to investments in transmission affiliates |  |  |  |
Investment in transmission affiliates, balance at beginning of period | 1,921.7 | 1,818.2 | 1,909.2 | 1,789.4
Add: Earnings from equity method investment | 43.6 | 43.0 | 87.4 | 84.7
Add: Capital contributions | 27.2 | 9.2 | 33.3 | 30.3
Less: Distributions | 36.6 | 33.2 | 74.0 | 67.2
Investment in transmission affiliates, balance at end of period | $ 1,955.9 | 1,837.2 | $ 1,955.9 | 1,837.2
ATC |  |  |  |
Investment in transmission affiliates |  |  |  |
Equity method investment, ownership interest (as a percent) | 60.00% |  | 60.00% |
Changes to investments in transmission affiliates |  |  |  |
Investment in transmission affiliates, balance at beginning of period | $ 1,896.2 | 1,795.0 | $ 1,884.6 | 1,766.9
Add: Earnings from equity method investment | 43.1 | 42.6 | 86.0 | 83.6
Add: Capital contributions | 27.2 | 9.2 | 33.3 | 30.3
Less: Distributions | 34.7 | 33.2 | 72.1 | 67.2
Investment in transmission affiliates, balance at end of period | $ 1,931.8 | 1,813.6 | $ 1,931.8 | 1,813.6
ATC Holdco |  |  |  |
Investment in transmission affiliates |  |  |  |
Equity method investment, ownership interest (as a percent) | 75.00% |  | 75.00% |
Changes to investments in transmission affiliates |  |  |  |
Investment in transmission affiliates, balance at beginning of period | $ 25.5 | 23.2 | $ 24.6 | 22.5
Add: Earnings from equity method investment | 0.5 | 0.4 | 1.4 | 1.1
Add: Capital contributions | 0.0 | 0.0 | 0.0 | 0.0
Less: Distributions | 1.9 | 0.0 | 1.9 | 0.0
Investment in transmission affiliates, balance at end of period | $ 24.1 | $ 23.6 | $ 24.1 | $ 23.6

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