Condensed Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Gains on settlement, tax	$ 0.0	$ 0.0	$ 7.6	$ 0.0

Amount of tax expense (benefit), before reclassification adjustments, related to increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

No definition available.

Name:	wec_OtherComprehensiveIncomeRealizedGainLossOnDerivativesArisingDuringPeriodTax
Namespace Prefix:	wec_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration