Schedule I - Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Carrying amount
Notes to parent company financial statements
Long-term debt, including current portion	$ 16,631.1	$ 15,464.2
Fair value
Notes to parent company financial statements
Long-term debt, including current portion	15,564.3	13,921.3
Long-term debt, including current portion	16,631.1	15,464.2
WEC Energy Group | Carrying amount
Notes to parent company financial statements
Long-term debt, including current portion	5,792.8	4,447.2
WEC Energy Group | Carrying amount | WECI
Notes to parent company financial statements
Long-term notes receivable from WECI	430.0	0.0
WEC Energy Group | Fair value
Notes to parent company financial statements
Long-term debt, including current portion	5,596.0	4,095.6
WEC Energy Group | Fair value | WECI
Notes to parent company financial statements
Long-term notes receivable from WECI	$ 425.7	$ 0.0