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Schedule I - Fair Value Measurements (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Notes to parent company financial statements |  |
Long-term debt, including current portion | $ 12,450.5 | $ 11,858.3
Carrying amount |  |
Notes to parent company financial statements |  |
Long-term debt, including current portion | 12,450.5 | 11,858.3
Fair value |  |
Notes to parent company financial statements |  |
Long-term debt, including current portion | 14,343.2 | 13,035.9
WEC Energy Group | Carrying amount |  |
Notes to parent company financial statements |  |
Long-term debt, including current portion | 2,754.8 | 2,541.6
WEC Energy Group | Fair value |  |
Notes to parent company financial statements |  |
Long-term debt, including current portion | $ 2,836.9 | $ 2,619.4

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