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