Schedule I - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 37.5	$ 84.5	$ 38.9
Other	68.0	77.2
Current assets	2,093.6	2,247.6
Long-term assets
Other	957.8	704.1
Long-term assets	32,858.2	31,228.2
Total assets	34,951.8	33,475.8	31,590.5
Current liabilities
Short-term debt	830.8	1,440.1
Current portion of long-term debt	686.9	360.1
Other	550.8	464.8
Current liabilities	3,182.7	3,331.7
Long-term liabilities
Long-term debt	11,171.4	9,975.6
Other	1,128.9	1,108.1
Long-term liabilities	21,514.5	20,301.4
Equity
Total liabilities and equity	34,951.8	33,475.8
WEC Energy Group
Current assets
Cash and cash equivalents	0.5	32.8	$ 4.0	$ 1.2
Accounts receivable from related parties	0.7	4.0
Notes receivable from related parties	22.5	71.0
Prepaid taxes	46.5	0.0
Other	0.0	0.6
Current assets	70.2	108.4
Long-term assets
Investments in subsidiaries	13,433.1	12,682.5
Notes receivable from UMERC	0.0	150.0
Other	23.0	31.8
Long-term assets	13,456.1	12,864.3
Total assets	13,526.3	12,972.7
Current liabilities
Short-term debt	334.7	548.4
Current portion of long-term debt	400.0	0.0
Accounts payable to related parties	2.5	7.7
Notes payable to related parties	489.3	398.9
Other	17.9	14.0
Current liabilities	1,244.4	969.0
Long-term liabilities
Long-term debt	2,141.6	2,190.8
Other	26.9	24.0
Long-term liabilities	2,168.5	2,214.8
Equity
Common shareholders' equity	10,113.4	9,788.9
Total liabilities and equity	$ 13,526.3	$ 12,972.7