Acquisitions - Consideration Transferred for Integrys Acquisition (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Jun. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Jun. 29, 2015
Business Acquisition [Line Items]
Integrys common shares outstanding at June 29, 2015		315,614,941	315,683,496
ATC
Business Acquisition [Line Items]
Equity interest in ATC				60.00%
Integrys
Business Acquisition [Line Items]
Percentage of Integrys common shares acquired				100.00%
Integrys common shares outstanding at June 29, 2015				79,963,091
Exchange ratio	1.128
Wisconsin Energy Corporation shares issued for Integrys shares	90,187,884
Closing price of Wisconsin Energy Corporation 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
Number of Wisconsin Energy Corporation fractional shares that were paid in cash				10,483
Dollar value of Wisconsin Energy Corporation fractional shares paid in cash				$ 0.5
Integrys | ATC
Business Acquisition [Line Items]
Equity interest in ATC		34.00%