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Acquisition (Details) (USD $)
In Billions, except Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Business Combinations [Abstract]  
Business Acquisition, Date of Acquisition Agreement Jun. 22, 2014
Estimate of acquisition-related debt $ 1.5wec_Estimateofacquisitionrelateddebt
Number of WEC shares per Integrys share 1.128wec_NumberofWECsharesperIntegrysshare
Cash per share of Integrys common stock $ 18.58wec_CashpershareofIntegryscommonstock
Estimate of number of WEC shares to be issued for acquisition 91,000,000wec_EstimateofnumberofWECsharestobeissuedforacquisition