Segment Information (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Financial information of reportable operating segments
Operating Revenues	[1]	$ 991.2	$ 1,043.7	$ 2,379.1	$ 2,738.7
Other operation and maintenance		337.0	256.0	617.7	531.4
Depreciation and Amortization		105.7	101.4	210.8	202.0
Operating Income (Loss)		165.8	240.7	524.6	622.5
Equity in Earnings of Unconsolidated Affiliates		14.2	17.5	30.3	34.8
Interest Expense, net		62.1	59.0	121.8	121.3
Income Tax Expense (Benefit)		63.2	74.3	185.6	204.6
Net Income (Loss)		80.9	133.0	276.7	340.6
Capital Expenditures		207.0	176.3	356.5	305.5
Reportable Operating Segments Energy Utility [Member]
Financial information of reportable operating segments
Operating Revenues	[1]	979.9	1,029.8	2,356.8	2,711.9
Other operation and maintenance		368.3	343.6	737.4	711.2
Depreciation and Amortization		88.5	84.3	176.4	167.9
Operating Income (Loss)		140.4	155.2	416.9	447.9
Equity in Earnings of Unconsolidated Affiliates		14.3	17.5	30.4	34.8
Interest Expense, net		32.4	30.7	64.1	64.7
Income Tax Expense (Benefit)		44.0	51.4	141.8	158.8
Net Income (Loss)		82.1	96.3	247.2	265.7
Capital Expenditures		201.0	172.6	345.2	293.3
Reportable Operating Segments Energy Non Utility [Member]
Financial information of reportable operating segments
Operating Revenues	[1]	115.3	113.4	225.0	221.7
Other operation and maintenance		4.7	5.0	5.8	6.2
Depreciation and Amortization		17.1	16.7	34.1	33.6
Operating Income (Loss)		93.5	91.7	185.1	181.9
Equity in Earnings of Unconsolidated Affiliates		0.0	0.0	0.0	0.0
Interest Expense, net		15.9	16.2	31.8	32.5
Income Tax Expense (Benefit)		38.4	30.2	69.0	60.2
Net Income (Loss)		39.5	45.4	84.7	89.5
Capital Expenditures		3.2	4.6	7.2	9.7
Corporate and Other [Member]
Financial information of reportable operating segments
Operating Revenues	[1],[2]	0.5	0.3	0.8	0.6
Other operation and maintenance	[2]	68.1	6.1	77.5	7.3
Depreciation and Amortization	[2]	0.1	0.4	0.3	0.5
Operating Income (Loss)	[2]	(68.1)	(6.2)	(77.4)	(7.3)
Equity in Earnings of Unconsolidated Affiliates	[2]	(0.1)	0.0	(0.1)	0.0
Interest Expense, net	[2]	14.0	12.2	26.2	24.4
Income Tax Expense (Benefit)	[2]	(19.2)	(7.3)	(25.2)	(14.4)
Net Income (Loss)	[2]	82.1	132.9	279.1	340.4
Capital Expenditures	[2]	2.8	(0.9)	4.1	2.5
Eliminations and Reconciling Items [Member]
Financial information of reportable operating segments
Operating Revenues	[1]	(104.5)	(99.8)	(203.5)	(195.5)
Other operation and maintenance		(104.1)	(98.7)	(203.0)	(193.3)
Depreciation and Amortization		0.0	0.0	0.0	0.0
Operating Income (Loss)		0.0	0.0	0.0	0.0
Equity in Earnings of Unconsolidated Affiliates		0.0	0.0	0.0	0.0
Interest Expense, net		(0.2)	(0.1)	(0.3)	(0.3)
Income Tax Expense (Benefit)		0.0	0.0	0.0	0.0
Net Income (Loss)		(122.8)	(141.6)	(334.3)	(355.0)
Capital Expenditures		$ 0.0	$ 0.0	$ 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.