Acquisition Consideration Transferred (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Jun. 30, 2015	Jun. 29, 2015
Acquisition
Percentage of Integrys common shares acquired		100.00%
WEC interest in ATC	60.00%	60.00%
Exchange ratio	1.128
Wisconsin Energy Shares issued for Integrys shares	90,187,884
Number of Wisconsin Energy fractional shares that were paid in cash		10,483
Dollar value of Wisconsin Energy fractional shares paid in cash		$ 0.5
Closing price of Wisconsin Energy common shares on June 29, 2015		$ 45.16
Fair value of common stock issued		$ 4,072.9
Cash paid per share of Integrys shares outstanding	$ 18.58
Fair value of cash paid for integrys shares		1,486.2
Consideration attributable to settlement of equity awards, net of tax		24.0
Total cash consideration paid for acquisition		$ 1,510.2
Total purchase price	$ 5,583.1
Integrys
Acquisition
WEC interest in ATC		34.00%
Integrys common shares outstanding at June 29, 2015		79,963,091