Condensed Parent Company Financial Statements (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Operating Activities
Net income	$ 526.2	$ 456.5	$ 382.4
Reconciliation to cash
Equity in susidiaries' earnings	(62.5)	(60.1)	(59.1)
Deferred income taxes, net	434.8	108.6	191.2
Accrued income taxes, net	(87.4)	(42.7)	43.4
Other current assets	(20.5)	14.1	24.8
Other current liabilities	44.1	22.0	(11.7)
Accounts receivable and accrued revenues	30.1	(50.4)	111.1
Other, net	(27.0)	40.0	(29.6)
Cash Provided by Operating Activities	993.4	810.4	628.9
Investing Activities
Proceeds from asset sales	41.5	68.7	16.8
Capital contributions to associated companies	(6.6)	(5.2)	(25.9)
Cash Used in Investing Activities	(892.5)	(633.5)	(736.1)
Financing Activities
Exercise of stock options	54.4	90.9	17.0
Purchase of common stock	(193.9)	(156.6)	(29.6)
Dividends paid on common stock	(242.0)	(187.0)	(157.8)
Issuance of long-term debt	720.0	530.0	261.5
Retirement and repurchase of long-term debt	(466.6)	(291.7)	(221.1)
Change in short-term debt	12.0	(167.2)	222.8
Other, net	4.8	9.0	2.9
Cash (Used in) Provided by Financing Activities	(111.3)	(172.6)	95.7
Change in Cash and Cash Equivalents	(10.4)	4.3	(11.5)
Cash and Cash Equivalents at Beginning of Year	24.5	20.2	31.7
Cash and Cash Equivalents at End of Year	14.1	24.5	20.2
Wisconsin Energy Corporation [Member]
Operating Activities
Net income	526.2	456.5	382.4
Reconciliation to cash
Equity in susidiaries' earnings	(545.9)	(482.9)	(397.7)
Dividends and distributions from subsidiaries	995.5	305.3	225.2
Deferred income taxes, net	(350.9)	(29.7)	28.2
Accrued income taxes, net	363.4	41.9	(15.5)
Other current assets	(0.1)	11.5	8.1
Other current liabilities	8.9	3.0	(0.4)
Accounts receivable and accrued revenues	(18.7)	477.2	1.7
Other, net	(10.2)	(1.4)	6.6
Cash Provided by Operating Activities	968.2	781.4	238.6
Investing Activities
Proceeds from asset sales	0	63.1	0
Capital contributions to associated companies	(36.5)	(64.5)	(108.9)
Capitalized interest and other	2.4	(57.3)	(42.7)
Cash Used in Investing Activities	(34.1)	(58.7)	(151.6)
Financing Activities
Exercise of stock options	54.4	90.9	17.0
Purchase of common stock	(193.9)	(156.6)	(29.6)
Dividends paid on common stock	(242.0)	(187.0)	(157.8)
Issuance of long-term debt	0	0	11.4
Retirement and repurchase of long-term debt	(450.0)	(281.5)	0
Change in short-term debt	(116.5)	(310.5)	74.0
Change in notes payable due associated companies	3.9	106.1	(6.6)
Other, net	9.9	15.8	3.4
Cash (Used in) Provided by Financing Activities	(934.2)	(722.8)	(88.2)
Change in Cash and Cash Equivalents	(0.1)	(0.1)	(1.2)
Cash and Cash Equivalents at Beginning of Year	0.6	0.7	1.9
Cash and Cash Equivalents at End of Year	$ 0.5	$ 0.6	$ 0.7

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Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits are not generally reported as cash and cash equivalents. Includes cash and cash equivalents associated with the entity's continuing operations. Excludes cash and cash equivalents associated with the disposal group (and discontinued operation).