Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Financial information of reportable operating segments
Operating Revenues	$ 944.7	[1]	$ 991.7	[1]	$ 2,135.9	[1]	$ 2,320.4	[1]
Other operation and maintenance	267.9		298.9		554.2		612.4
Depreciation and Amortization	90.3		82.3		177.9		163.6
Operating Income (Loss)	222.6		174.4		518.3		470.0
Equity in Earnings of Unconsolidated Affiliates	16.1		15.1		31.7		30.5
Interest Expense, net	61.5		57.4		120.4		120.8
Income Tax Expense (Benefit)	66.6		48.6		162.9		137.9
Income (Loss) from Discontinued Operations, Net of Tax	0		11.5		0		11.5
Net Income (Loss)	119.3		109.5		291.4		280.4
Capital Expenditures	171.7		211.6		314.0		347.1
Reportable Operating Segments Energy Utility [Member]
Financial information of reportable operating segments
Operating Revenues	930.5	[1]	977.9	[1]	2,108.9	[1]	2,294.4	[1]
Other operation and maintenance	358.5		388.8		734.9		789.7
Depreciation and Amortization	73.4		63.9		144.1		127.3
Operating Income (Loss)	133.6		88.1		342.2		301.1
Equity in Earnings of Unconsolidated Affiliates	16.2		15.2		31.8		30.7
Interest Expense, net	32.0		27.2		61.2		55.3
Income Tax Expense (Benefit)	43.0		29.1		117.0		100.4
Income (Loss) from Discontinued Operations, Net of Tax	0		0		0		0
Net Income (Loss)	82.7		61.1		218.9		202.1
Capital Expenditures	169.4		203.8		307.0		331.0
Reportable Operating Segments Energy Non Utility [Member]
Financial information of reportable operating segments
Operating Revenues	112.3	[1]	111.3	[1]	219.6	[1]	214.5	[1]
Other operation and maintenance	5.3		5.1		7.4		6.6
Depreciation and Amortization	16.7		18.3		33.5		36.0
Operating Income (Loss)	90.3		87.9		178.7		171.9
Equity in Earnings of Unconsolidated Affiliates	0		0		0		0
Interest Expense, net	16.7		17.0		33.5		32.9
Income Tax Expense (Benefit)	29.2		28.1		58.0		55.8
Income (Loss) from Discontinued Operations, Net of Tax	0		0		0		0
Net Income (Loss)	44.4		42.8		87.4		83.3
Capital Expenditures	1.9		6.7		3.8		14.9
Corporate and Other [Member]
Financial information of reportable operating segments
Operating Revenues	0.3	[1],[2]	0.2	[1],[2]	0.6	[1],[2]	0.4	[1],[2]
Other operation and maintenance	1.4	[2]	1.7	[2]	2.7	[2]	2.8	[2]
Depreciation and Amortization	0.2	[2]	0.1	[2]	0.3	[2]	0.3	[2]
Operating Income (Loss)	(1.3)	[2]	(1.6)	[2]	(2.6)	[2]	(3.0)	[2]
Equity in Earnings of Unconsolidated Affiliates	(0.1)	[2]	(0.1)	[2]	(0.1)	[2]	(0.2)	[2]
Interest Expense, net	12.9	[2]	13.3	[2]	26.0	[2]	32.8	[2]
Income Tax Expense (Benefit)	(5.6)	[2]	(8.6)	[2]	(12.1)	[2]	(18.3)	[2]
Income (Loss) from Discontinued Operations, Net of Tax	0	[2]	11.5	[2]	0	[2]	11.5	[2]
Net Income (Loss)	119.3	[2]	109.5	[2]	291.9	[2]	280.3	[2]
Capital Expenditures	0.4	[2]	1.1	[2]	3.2	[2]	1.2	[2]
Eliminations and Reconciling Items [Member]
Financial information of reportable operating segments
Operating Revenues	(98.4)	[1]	(97.7)	[1]	(193.2)	[1]	(188.9)	[1]
Other operation and maintenance	(97.3)		(96.7)		(190.8)		(186.7)
Depreciation and Amortization	0		0		0		0
Operating Income (Loss)	0		0		0		0
Equity in Earnings of Unconsolidated Affiliates	0		0		0		0
Interest Expense, net	(0.1)		(0.1)		(0.3)		(0.2)
Income Tax Expense (Benefit)	0		0		0		0
Income (Loss) from Discontinued Operations, Net of Tax	0		0		0		0
Net Income (Loss)	(127.1)		(103.9)		(306.8)		(285.3)
Capital Expenditures	$ 0		$ 0		$ 0		$ 0

[1] An elimination for intersegment revenues is included in Operating Revenues. This elimination is primarily between We Power and Wisconsin Electric.

[2] Corporate & Other includes all other non-utility activities, primarily non-utility real estate investment and development by Wispark as well as interest on corporate debt.