Short-Term Debt and Lines of Credit - Credit Facilities (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) extension	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Subsidiary note payable to WEC Energy Group	$ 18.5	$ 19.6
Letters of Credit Issued Inside Credit Facilities	18.0
Available capacity under existing agreements	$ 323.0
Number of extensions available on a credit facility | extension	2
Length of credit facility extension	1 year
Credit facility maturing December 2020
Line of Credit Facility [Line Items]
Short-term credit capacity	$ 500.0
Bostco | WEC Energy Group
Line of Credit Facility [Line Items]
Subsidiary note payable to WEC Energy Group	$ 18.5
Note payable, related party, interest rate	5.17%
Commercial Paper
Line of Credit Facility [Line Items]
Short-term debt outstanding	$ 159.0	$ 144.0