Segment Reporting (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Financial information of reportable operating segments
Operating Revenues	$ 4,519.0	[1]	$ 4,246.4	[1]	$ 4,486.4	[1]
Depreciation and Amortization	388.1		364.2		330.2
Operating Income (Loss)	1,080.1		1,000.3		887.3
Equity in Earnings of Unconsolidated Affiliates	68.4		65.5		61.6
Interest Expense, net	252.1		248.2		235.8
Income Tax Expense (Benefit)	337.9		306.3		263.9
Income from Discontinued Operations, Net of Tax	0		0		13.4
Net Income (Loss)	577.4		546.3		526.2
Capital Expenditures	687.4		707.0		830.8
Total Assets	(14,769.4)	[2]	(14,285.0)	[2]	(13,862.1)	[2]
Utility Energy [Member]
Financial information of reportable operating segments
Operating Revenues	4,462.0	[1]	4,190.8	[1]	4,431.5	[1]
Depreciation and Amortization	320.2		296.4		257.0
Operating Income (Loss)	719.4		647.7		544.8
Equity in Earnings of Unconsolidated Affiliates	68.5		65.7		62.5
Interest Expense, net	136.2		129.4		110.0
Income Tax Expense (Benefit)	243.6		214.9		182.7
Income from Discontinued Operations, Net of Tax					0
Net Income (Loss)	425.1		400.6		376.3
Capital Expenditures	657.9		697.3		792.2
Total Assets	(14,460.4)	[2]	(13,988.1)	[2]	(13,433.5)	[2]
Non-Utility Energy [Member]
Financial information of reportable operating segments
Operating Revenues	446.7	[1]	439.9	[1]	435.1	[1]
Depreciation and Amortization	67.1		67.1		72.5
Operating Income (Loss)	367.1		358.8		348.9
Equity in Earnings of Unconsolidated Affiliates	0		0		0
Interest Expense, net	65.7		66.7		66.7
Income Tax Expense (Benefit)	120.2		116.6		112.8
Income from Discontinued Operations, Net of Tax					0
Net Income (Loss)	181.6		175.9		169.8
Capital Expenditures	26.1		5.5		31.2
Total Assets	(2,846.5)	[2]	(2,903.5)	[2]	(2,949.0)	[2]
Corporate and Other [Member]
Financial information of reportable operating segments
Operating Revenues	1.3	[1],[3]	1.2	[1],[3]	0.9	[1],[3]
Depreciation and Amortization	0.8	[3]	0.7	[3]	0.7	[3]
Operating Income (Loss)	(6.4)	[3]	(6.2)	[3]	(6.4)	[3]
Equity in Earnings of Unconsolidated Affiliates	(0.1)	[3]	(0.2)	[3]	(0.9)	[3]
Interest Expense, net	50.8	[3]	52.5	[3]	59.5	[3]
Income Tax Expense (Benefit)	(25.9)	[3]	(25.2)	[3]	(31.6)	[3]
Income from Discontinued Operations, Net of Tax					13.4	[3]
Net Income (Loss)	577.2	[3]	546.1	[3]	525.9	[3]
Capital Expenditures	3.4	[3]	4.2	[3]	7.4	[3]
Total Assets	(4,719.5)	[2],[3]	(4,431.4)	[2],[3]	(4,694.8)	[2],[3]
Reconciling Items [Member]
Financial information of reportable operating segments
Operating Revenues	(391.0)	[1]	(385.5)	[1]	(381.1)	[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	(0.6)		(0.4)		(0.4)
Income Tax Expense (Benefit)	0		0		0
Income from Discontinued Operations, Net of Tax					0
Net Income (Loss)	(606.5)		(576.3)		(545.8)
Capital Expenditures	0		0		0
Total Assets	7,257.0	[2]	7,038.0	[2]	7,215.2	[2]
Elimination [Member]
Financial information of reportable operating segments
Total Assets	$ 2,231.2		$ 2,286.7		$ 2,369.0

[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 $2,231.2 million, $2,286.7 million and $2,369.0 million is included in Total Assets as of December 31, 2013, 2012 and 2011, 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.