Segment Reporting (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Financial information of reportable operating segments
Operating Revenues	$ 4,246.4	[1]	$ 4,486.4	[1]	$ 4,202.5	[1]
Depreciation and Amortization	364.2		330.2		305.6
Operating Income (Loss)	1,000.3		887.3		810.4
Equity in Earnings of Unconsolidated Affiliates	65.5		61.6		59.9
Interest Expense, net	248.2		235.8		206.4
Income Tax Expense (Benefit)	306.3		263.9		249.9
Income from Discontinued Operations, Net of Tax	0		13.4		2.1
Net Income (Loss)	546.3		526.2		456.5
Capital Expenditures	707.0		830.8		798.2
Total Assets	(14,285.0)	[2]	(13,862.1)	[2]	(13,059.8)	[2]
Utility Energy [Member]
Financial information of reportable operating segments
Operating Revenues	4,190.8	[1]	4,431.5	[1]	4,165.3	[1]
Depreciation and Amortization	296.4		257.0		251.4
Operating Income (Loss)	647.7		544.8		564.0
Equity in Earnings of Unconsolidated Affiliates	65.7		62.5		60.1
Interest Expense, net	129.4		110.0		117.2
Income Tax Expense (Benefit)	214.9		182.7		192.1
Income from Discontinued Operations, Net of Tax	0		0		0.7
Net Income (Loss)	400.6		376.3		354.2
Capital Expenditures	697.3		792.2		687.0
Total Assets	(13,988.1)	[2]	(13,433.5)	[2]	(11,997.4)	[2]
Non-Utility Energy [Member]
Financial information of reportable operating segments
Operating Revenues	439.9	[1]	435.1	[1]	320.2	[1]
Depreciation and Amortization	67.1		72.5		53.5
Operating Income (Loss)	358.8		348.9		252.4
Equity in Earnings of Unconsolidated Affiliates	0		0		0
Interest Expense, net	66.7		66.7		40.3
Income Tax Expense (Benefit)	116.6		112.8		84.9
Income from Discontinued Operations, Net of Tax	0		0		0
Net Income (Loss)	175.9		169.8		128.4
Capital Expenditures	5.5		31.2		109.3
Total Assets	(2,903.5)	[2]	(2,949.0)	[2]	(2,914.2)	[2]
Corporate and Other [Member]
Financial information of reportable operating segments
Operating Revenues	1.2	[1],[3]	0.9	[1],[3]	0.5	[1],[3]
Depreciation and Amortization	0.7	[3]	0.7	[3]	0.7	[3]
Operating Income (Loss)	(6.2)	[3]	(6.4)	[3]	(6.0)	[3]
Equity in Earnings of Unconsolidated Affiliates	(0.2)	[3]	(0.9)	[3]	(0.2)	[3]
Interest Expense, net	52.5	[3]	59.5	[3]	52.8	[3]
Income Tax Expense (Benefit)	(25.2)	[3]	(31.6)	[3]	(27.1)	[3]
Income from Discontinued Operations, Net of Tax	0	[3]	13.4	[3]	1.4	[3]
Net Income (Loss)	546.1	[3]	525.9	[3]	456.4	[3]
Capital Expenditures	4.2	[3]	7.4	[3]	1.9	[3]
Total Assets	(4,431.4)	[2],[3]	(4,694.8)	[2],[3]	(5,075.9)	[2],[3]
Reconciling Items [Member]
Financial information of reportable operating segments
Operating Revenues	(385.5)	[1]	(381.1)	[1]	(283.5)	[1]
Depreciation and Amortization	0		0		0
Operating Income (Loss)	0		0		0
Equity in Earnings of Unconsolidated Affiliates	0		0		0
Interest Expense, net	(0.4)		(0.4)		(3.9)
Income Tax Expense (Benefit)	0		0		0
Income from Discontinued Operations, Net of Tax	0		0		0
Net Income (Loss)	(576.3)		(545.8)		(482.5)
Capital Expenditures	0		0		0
Total Assets	7,038.0	[2]	7,215.2	[2]	6,927.7	[2]
Elimination [Member]
Financial information of reportable operating segments
Total Assets	$ 2,286.7		$ 2,369.0		$ 1,785.9

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

[2] An elimination of $2,286.7 million, $2,369.0 million and $1,785.9 million is included in Total Assets as of December 31, 2012, 2011 and 2010, respectively, for all PTF-related activity between We Power and Wisconsin Electric.

[3] 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.