Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Financial information of reportable operating segments
Operating Revenues	$ 1,695.0	[1]	$ 1,275.2	[1]
Other operation and maintenance	275.4		288.1
Depreciation and Amortization	100.6		95.5
Operating Income (Loss)	381.8		321.0
Equity in Earnings of Unconsolidated Affiliates	17.3		16.7
Interest Expense, net	62.3		65.0
Income Tax Expense (Benefit)	130.3		100.4
Net Income (Loss)	207.6		176.6
Capital Expenditures	129.2		133.6
Reportable Operating Segments Energy Utility [Member]
Financial information of reportable operating segments
Operating Revenues	1,682.1	[1]	1,261.5	[1]
Other operation and maintenance	367.6		380.6
Depreciation and Amortization	83.6		78.6
Operating Income (Loss)	292.7		230.6
Equity in Earnings of Unconsolidated Affiliates	17.3		16.6
Interest Expense, net	34.0		35.9
Income Tax Expense (Benefit)	107.4		77.4
Net Income (Loss)	169.4		138.0
Capital Expenditures	120.7		130.9
Reportable Operating Segments Energy Non Utility [Member]
Financial information of reportable operating segments
Operating Revenues	108.3	[1]	109.8	[1]
Other operation and maintenance	1.2		1.5
Depreciation and Amortization	16.9		16.7
Operating Income (Loss)	90.2		91.6
Equity in Earnings of Unconsolidated Affiliates	0		0
Interest Expense, net	16.3		16.5
Income Tax Expense (Benefit)	30.0		30.5
Net Income (Loss)	44.1		44.6
Capital Expenditures	5.1		2.1
Corporate and Other [Member]
Financial information of reportable operating segments
Operating Revenues	0.3	[1],[2]	0.3	[1],[2]
Other operation and maintenance	1.2	[2]	1.0	[2]
Depreciation and Amortization	0.1	[2]	0.2	[2]
Operating Income (Loss)	(1.1)	[2]	(1.2)	[2]
Equity in Earnings of Unconsolidated Affiliates	0	[2]	0.1	[2]
Interest Expense, net	12.2	[2]	12.8	[2]
Income Tax Expense (Benefit)	(7.1)	[2]	(7.5)	[2]
Net Income (Loss)	207.5	[2]	176.6	[2]
Capital Expenditures	3.4	[2]	0.6	[2]
Eliminations and Reconciling Items [Member]
Financial information of reportable operating segments
Operating Revenues	(95.7)	[1]	(96.4)	[1]
Other operation and maintenance	(94.6)		(95.0)
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)	(213.4)		(182.6)
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.