Condensed Parent Company Financial Statements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Condensed Parent Company Income Statement
Other Income, Net	$ 62.7	$ 40.2	$ 28.5
Interest Expense, net	235.8	206.4	156.7
Income (Loss) from Continuing Operations Before Income Taxes	776.7	704.3	591.2
Income Tax Benefit	(263.9)	(249.9)	(215.5)
Income from Continuing Operations	512.8	454.4	375.7
Income from Discontinued Operations, Net of Tax	13.4	2.1	6.7
Net Income	526.2	456.5	382.4
Subsidiaries [Member]
Condensed Parent Company Income Statement
Income from Continuing Operations	545.9	482.1	395.9
Income from Discontinued Operations, Net of Tax	13.4	2.1	6.7
Wisconsin Energy Corporation [Member]
Condensed Parent Company Income Statement
Other Income, Net	2.7	4.2	24.2
Corporate Expense	4.8	4.0	8.9
Interest Expense, net	61.8	53.8	50.2
Income (Loss) from Continuing Operations Before Income Taxes	(63.9)	(53.6)	(34.9)
Income Tax Benefit	30.8	25.9	14.7
Income from Continuing Operations	(33.1)	(27.7)	(20.2)
Net Income	$ 526.2	$ 456.5	$ 382.4