Condensed Parent Company Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities
Net income	$ 588.3	$ 577.4	$ 546.3
Reconciliation to cash
Deferred income taxes, net	329.2	313.8	294.4
Accrued income taxes, net	(11.4)	36.6	116.9
Other current assets	(13.9)	2.8	12.1
Other current liabilities	(18.8)	7.2	(14.9)
Accounts receivable and accrued revenues	80.7	(162.9)	38.3
Other, net	(112.1)	49.2	(164.0)
Cash Provided by Operating Activities	1,197.7	1,231.0	1,173.9
Investing Activities
Proceeds from asset sales	13.9	2.5	8.7
Capital contributions to associated companies	(13.1)	(10.5)	(15.7)
Cash Used in Investing Activities	(756.8)	(745.8)	(729.6)
Financing Activities
Exercise of stock options	50.3	48.5	49.8
Purchase of common stock	(123.2)	(223.4)	(153.2)
Dividends paid on common stock	(352.0)	(328.9)	(276.3)
Issuance of long-term debt	250.0	251.0	251.8
Retirement and repurchase of long-term debt	(324.3)	(397.2)	(20.3)
Change in short-term debt	80.2	142.8	(275.3)
Other, net	14.0	12.4	0.7
Cash Used in Financing Activities	(405.0)	(494.8)	(422.8)
Change in Cash and Cash Equivalents	35.9	(9.6)	21.5
Cash and Cash Equivalents at Beginning of Year	26.0	35.6	14.1
Cash and Cash Equivalents at End of Year	61.9	26.0	35.6
Wisconsin Energy Corporation [Member]
Operating Activities
Net income	588.3	577.4	546.3
Reconciliation to cash
Equity in susidiaries' earnings	(635.0)	(607.8)	(577.6)
Dividends and distributions from subsidiaries	720.0	720.4	842.3
Deferred income taxes, net	60.1	(7.8)	104.4
Accrued income taxes, net	4.1	66.8	(457.9)
Other current assets	0	(0.1)	0.2
Other current liabilities	5.1	(22.9)	(6.7)
Accounts receivable and accrued revenues	(0.3)	(2.7)	22.5
Other, net	(8.1)	(21.6)	(8.1)
Cash Provided by Operating Activities	734.2	701.7	465.4
Investing Activities
Capital contributions to associated companies	(225.5)	(195.3)	(21.5)
Capitalized interest and other	5.0	4.0	12.6
Cash Used in Investing Activities	(220.5)	(191.3)	(8.9)
Financing Activities
Exercise of stock options	50.3	48.5	49.8
Purchase of common stock	(123.2)	(223.4)	(153.9)
Dividends paid on common stock	(352.0)	(328.9)	(276.3)
Change in short-term debt	(72.0)	5.0	(79.5)
Change in notes payable due associated companies	3.5	(26.8)	3.8
Other, net	16.7	14.6	0
Cash Used in Financing Activities	(476.7)	(511.0)	(456.1)
Change in Cash and Cash Equivalents	37.0	(0.6)	0.4
Cash and Cash Equivalents at Beginning of Year	0.3	0.9	0.5
Cash and Cash Equivalents at End of Year	$ 37.3	$ 0.3	$ 0.9