Schedule I - Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Carrying amount
Notes to parent company financial statements
Long-term debt, including current portion	$ 18,907.1	$ 16,631.1
Fair value
Notes to parent company financial statements
Long-term debt, including current portion	17,840.8	15,564.3
Long-term debt, including current portion	18,907.1	16,631.1
WEC Energy Group | Carrying amount
Notes to parent company financial statements
Long-term debt, including current portion	6,755.4	5,792.8
WEC Energy Group | Carrying amount | WECI
Notes to parent company financial statements
Long-term notes receivable from WECI	300.0	430.0
WEC Energy Group | Fair value
Notes to parent company financial statements
Long-term debt, including current portion	6,776.0	5,596.0
WEC Energy Group | Fair value | WECI
Notes to parent company financial statements
Long-term notes receivable from WECI	$ 300.0	$ 425.7