Schedule I - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 24.8	$ 37.5	$ 84.5
Other	63.4	68.0
Current assets	2,083.0	2,093.6
Long-term assets
Other	896.5	957.8
Long-term assets	34,945.1	32,858.2
Total assets	37,028.1	34,951.8	33,475.8
Current liabilities
Current portion of long-term debt	777.7	686.9
Other	530.7	550.8
Current liabilities	4,148.1	3,182.7
Long-term liabilities
Long-term debt	11,672.8	11,171.4
Other	1,229.4	1,128.9
Long-term liabilities	22,217.5	21,514.5
Equity
Total liabilities and equity	37,028.1	34,951.8
WEC Energy Group
Current assets
Cash and cash equivalents	4.0	0.5	$ 32.8	$ 4.0
Accounts receivable from related parties	0.7	0.7
Notes receivable from related parties	110.8	22.5
Prepaid taxes	54.4	46.5
Other	0.1	0.0
Current assets	170.0	70.2
Long-term assets
Investments in subsidiaries	14,248.3	13,433.1
Other	15.7	23.0
Long-term assets	14,264.0	13,456.1
Total assets	14,434.0	13,526.3
Current liabilities
Short-term debt	820.4	334.7
Current portion of long-term debt	0.0	400.0
Accounts payable to related parties	31.7	2.5
Notes payable to related parties	303.0	489.3
Other	19.6	17.9
Current liabilities	1,174.7	1,244.4
Long-term liabilities
Long-term debt	2,754.8	2,141.6
Other	34.8	26.9
Long-term liabilities	2,789.6	2,168.5
Equity
Common shareholders' equity	10,469.7	10,113.4
Total liabilities and equity	$ 14,434.0	$ 13,526.3