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SHORT-TERM DEBT AND LINES OF CREDIT - SHORT-TERM BORROWINGS (Details) - USD ($) $ in Millions | 1 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | ---
Mar. 31, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Mar. 31, 2021 | Dec. 31, 2020
Short-term borrowings |  |  |  |  |
Issuance of term loan |  | $ 0.5 | $ 340.0 |  |
WEC Senior Notes 0.80% due 2024 | WEC Energy Group |  |  |  |  |
Short-term borrowings |  |  |  |  |
Debt instrument stated interest rate percentage |  |  |  | 0.80% |
Commercial paper |  |  |  |  |
Short-term borrowings |  |  |  |  |
Commercial paper outstanding |  | $ 1,508.4 |  |  | $ 1,436.9
Weighted average interest rate on amounts outstanding |  | 0.16% |  |  | 0.21%
Average amount of commercial paper outstanding during the period |  | $ 1,415.4 |  |  |
Weighted-average interest rate on amounts outstanding during the period |  | 0.17% |  |  |
Term loan |  |  |  |  |
Short-term borrowings |  |  |  |  |
Operating expense loans outstanding |  | $ 0.5 |  |  | $ 0.0
Term loan | WEC Energy Group |  |  |  |  |
Short-term borrowings |  |  |  |  |
Term loan outstanding |  | $ 0.0 |  |  | $ 340.0
Weighted average interest rate on amounts outstanding |  |  |  |  | 0.99%
Issuance of term loan | $ 340.0 |  |  |  |
Length of term loan | 364 days |  |  |  |

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