Schedule I - Short-Term Notes Payable to Related Parties (Details) - WEC Energy Group - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Notes to parent company financial statements
Short-term notes payable to related parties	$ 398.9	$ 406.0
Integrys
Notes to parent company financial statements
Short-term notes payable to related parties	139.5	278.2
WBS
Notes to parent company financial statements
Short-term notes payable to related parties	123.5	16.4
WECC
Notes to parent company financial statements
Short-term notes payable to related parties	110.3	110.2
Bluewater Gas Storage, LLC
Notes to parent company financial statements
Short-term notes payable to related parties	25.6	0.3
Wisvest
Notes to parent company financial statements
Short-term notes payable to related parties	$ 0.0	$ 0.9