Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Financial information of reportable operating segments
Operating Revenues	$ 1,275.2	[1]	$ 1,191.2	[1]
Other operation and maintenance	288.1		286.3
Depreciation and Amortization	95.5		87.6
Operating Income (Loss)	321.0		295.7
Equity in Earnings of Unconsolidated Affiliates	16.7		15.6
Interest Expense, net	65.0		58.9
Income Tax Expense (Benefit)	100.4		96.3
Net Income (Loss)	176.6		172.1
Capital Expenditures	133.6		142.3
Reportable Operating Segments Energy Utility [Member]
Financial information of reportable operating segments
Operating Revenues	1,261.5	[1]	1,178.4	[1]
Other operation and maintenance	380.6		376.4
Depreciation and Amortization	78.6		70.7
Operating Income (Loss)	230.6		208.6
Equity in Earnings of Unconsolidated Affiliates	16.6		15.6
Interest Expense, net	35.9		29.2
Income Tax Expense (Benefit)	77.4		74.0
Net Income (Loss)	138.0		136.2
Capital Expenditures	130.9		137.6
Reportable Operating Segments Energy Non Utility [Member]
Financial information of reportable operating segments
Operating Revenues	109.8	[1]	107.3	[1]
Other operation and maintenance	1.5		2.1
Depreciation and Amortization	16.7		16.8
Operating Income (Loss)	91.6		88.4
Equity in Earnings of Unconsolidated Affiliates	0		0
Interest Expense, net	16.5		16.8
Income Tax Expense (Benefit)	30.5		28.8
Net Income (Loss)	44.6		43.0
Capital Expenditures	2.1		1.9
Corporate and Other [Member]
Financial information of reportable operating segments
Operating Revenues	0.3	[1],[2]	0.3	[1],[2]
Other operation and maintenance	1.0	[2]	1.3	[2]
Depreciation and Amortization	0.2	[2]	0.1	[2]
Operating Income (Loss)	(1.2)	[2]	(1.3)	[2]
Equity in Earnings of Unconsolidated Affiliates	0.1	[2]	0	[2]
Interest Expense, net	12.8	[2]	13.1	[2]
Income Tax Expense (Benefit)	(7.5)	[2]	(6.5)	[2]
Net Income (Loss)	176.6	[2]	172.6	[2]
Capital Expenditures	0.6	[2]	2.8	[2]
Eliminations and Reconciling Items [Member]
Financial information of reportable operating segments
Operating Revenues	(96.4)	[1]	(94.8)	[1]
Other operation and maintenance	(95.0)		(93.5)
Depreciation and Amortization	0		0
Operating Income (Loss)	0		0
Equity in Earnings of Unconsolidated Affiliates	0		0
Interest Expense, net	(0.2)		(0.2)
Income Tax Expense (Benefit)	0		0
Net Income (Loss)	(182.6)		(179.7)
Capital Expenditures	$ 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 LLC, as well as interest on corporate debt.