Schedule I - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 84.5	$ 38.9	$ 37.5
Other	77.2	74.9
Current assets	2,247.6	2,213.5
Long-term assets
Other	704.1	619.9
Long-term assets	31,228.2	29,377.0
Total assets	33,475.8	31,590.5	30,123.2
Current liabilities
Short-term debt	1,440.1	1,444.6
Other	464.8	553.6
Current liabilities	3,331.7	3,869.3
Long-term liabilities
Other	1,108.1	1,206.3
Long-term liabilities	20,301.4	18,229.4
Equity
Total liabilities and equity	33,475.8	31,590.5
WEC Energy Group
Current assets
Cash and cash equivalents	32.8	4.0	$ 1.2	$ 1.3
Accounts receivable from related parties	4.0	1.9
Notes receivable from related parties	71.0	64.1
Prepaid taxes	0.0	17.5
Other	0.6	0.6
Current assets	108.4	88.1
Long-term assets
Investments in subsidiaries	12,682.5	12,101.9
Notes receivable from UMERC	150.0	50.0
Other	31.8	47.7
Long-term assets	12,864.3	12,199.6
Total assets	12,972.7	12,287.7
Current liabilities
Short-term debt	548.4	494.8
Current portion of long-term debt	0.0	300.0
Accounts payable to related parties	7.7	2.7
Notes payable to related parties	398.9	406.0
Other	14.0	8.9
Current liabilities	969.0	1,212.4
Long-term liabilities
Long-term debt	2,190.8	1,592.3
Other	24.0	21.6
Long-term liabilities	2,214.8	1,613.9
Equity
Common shareholders' equity	9,788.9	9,461.4
Total liabilities and equity	$ 12,972.7	$ 12,287.7