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SHORT-TERM DEBT AND LINES OF CREDIT - SHORT-TERM BORROWINGS (Details) - USD ($) $ in Millions		1 Months Ended	6 Months Ended
	Mar. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020
Short-term borrowings
Issuance of term loan			$ 0.0	$ 340.0
WEC Senior Notes 0.80% due 2024 \| WEC Energy Group
Short-term borrowings
Debt instrument stated interest rate percentage			0.80%		0.80%
Commercial paper
Short-term borrowings
Commercial paper outstanding			$ 1,424.5			$ 1,436.9
Weighted-average interest rate on amounts outstanding			0.17%			0.21%
Average amount outstanding during the period			$ 1,416.1
Weighted-average interest rate during the period			0.18%
Term loan \| WEC Energy Group
Short-term borrowings
Term loan outstanding			$ 0.0			$ 340.0
Weighted-average interest rate on amounts outstanding						0.99%
Weighted-average interest rate during the period			0.99%
Issuance of term loan	$ 340.0
Length of term loan	364 days	364 days