Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Financial information of reportable operating segments
Operating Revenues	$ 1,033.3	[1]	$ 1,053.2	[1]	$ 3,772.0	[1]	$ 3,340.7	[1]
Other operation and maintenance	249.4		268.1		780.8		821.6
Depreciation and Amortization	103.3		96.9		305.3		289.1
Operating Income (Loss)	246.1		258.0		868.6		808.5
Equity in Earnings of Unconsolidated Affiliates	18.0		17.1		52.8		51.0
Interest Expense, net	60.4		62.0		181.7		190.3
Income Tax Expense (Benefit)	80.3		80.7		284.9		251.4
Net Income (Loss)	126.3		137.5		466.9		433.1
Capital Expenditures	207.5		190.4		513.0		497.7
Reportable Operating Segments Energy Utility [Member]
Financial information of reportable operating segments
Operating Revenues	1,017.7	[1]	1,037.2	[1]	3,729.6	[1]	3,296.7	[1]
Other operation and maintenance	337.4		359.5		1,048.6		1,097.7
Depreciation and Amortization	86.3		79.9		254.2		238.2
Operating Income (Loss)	158.4		166.6		606.3		536.1
Equity in Earnings of Unconsolidated Affiliates	18.0		17.1		52.8		51.0
Interest Expense, net	32.1		33.0		96.8		103.1
Income Tax Expense (Benefit)	55.0		56.1		213.8		179.9
Net Income (Loss)	90.8		99.3		356.5		317.9
Capital Expenditures	188.2		178.1		481.5		476.2
Reportable Operating Segments Energy Non Utility [Member]
Financial information of reportable operating segments
Operating Revenues	114.1	[1]	114.2	[1]	335.8	[1]	337.3	[1]
Other operation and maintenance	3.5		4.2		9.7		10.6
Depreciation and Amortization	17.0		16.8		50.6		50.3
Operating Income (Loss)	93.6		93.2		275.5		276.4
Equity in Earnings of Unconsolidated Affiliates	0		0		0		0
Interest Expense, net	16.1		16.4		48.6		49.4
Income Tax Expense (Benefit)	30.4		29.5		90.6		90.1
Net Income (Loss)	47.3		47.4		136.8		137.2
Capital Expenditures	18.0		10.4		27.7		17.5
Corporate and Other [Member]
Financial information of reportable operating segments
Operating Revenues	0.3	[1],[2]	0.4	[1],[2]	0.9	[1],[2]	1.0	[1],[2]
Other operation and maintenance	6.0	[2]	1.9	[2]	13.3	[2]	4.1	[2]
Depreciation and Amortization	0	[2]	0.2	[2]	0.5	[2]	0.6	[2]
Operating Income (Loss)	(5.9)	[2]	(1.8)	[2]	(13.2)	[2]	(4.0)	[2]
Equity in Earnings of Unconsolidated Affiliates	0	[2]	0	[2]	0	[2]	0	[2]
Interest Expense, net	12.4	[2]	12.8	[2]	36.8	[2]	38.2	[2]
Income Tax Expense (Benefit)	(5.1)	[2]	(4.9)	[2]	(19.5)	[2]	(18.6)	[2]
Net Income (Loss)	126.3	[2]	137.4	[2]	466.7	[2]	432.9	[2]
Capital Expenditures	1.3	[2]	1.9	[2]	3.8	[2]	4.0	[2]
Eliminations and Reconciling Items [Member]
Financial information of reportable operating segments
Operating Revenues	(98.8)	[1]	(98.6)	[1]	(294.3)	[1]	(294.3)	[1]
Other operation and maintenance	(97.5)		(97.5)		(290.8)		(290.8)
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	(0.2)		(0.2)		(0.5)		(0.4)
Income Tax Expense (Benefit)	0		0		0		0
Net Income (Loss)	(138.1)		(146.6)		(493.1)		(454.9)
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 LLC, as well as interest on corporate debt.