DISCONTINUED OPERATIONS (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended					1 Months Ended	3 Months Ended					1 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013 Combined Locks	Mar. 31, 2012 Combined Locks	Dec. 31, 2012 Combined Locks	Mar. 31, 2013 WPS Beaver Falls Generation, LLC and WPS Syracuse Generation, LLC	Mar. 31, 2013 WPS Beaver Falls Generation, LLC and WPS Syracuse Generation, LLC	Mar. 31, 2012 WPS Beaver Falls Generation, LLC and WPS Syracuse Generation, LLC	Mar. 14, 2013 WPS Beaver Falls Generation, LLC and WPS Syracuse Generation, LLC	Dec. 31, 2012 WPS Beaver Falls Generation, LLC and WPS Syracuse Generation, LLC	Mar. 31, 2013 WPS Beaver Falls Generation, LLC and WPS Syracuse Generation, LLC Integrys Energy Services	Nov. 30, 2012 WPS Westwood Generation, LLC	Mar. 31, 2012 WPS Westwood Generation, LLC
Assets and liabilities classified as held for sale on balance sheets
Inventories			$ 0.5		$ 0.5				$ 1.8	$ 1.8
Other current assets									0.2
Property, plant, and equipment, net of accumulated depreciation			2.0		2.0				5.7	5.7
Accumulated depreciation			0.5		0.5
Other long-term assets									0.1	0.1
Total assets			2.5		2.5				7.8	7.6
Other current liabilities									0.4	0.2
Carrying value of the derivative contract liabilities assumed by the buyer											6.8
Components of discontinued operations recorded in income statements
Nonregulated revenues				0.4			1.2	(0.7)					4.1
Nonregulated cost of sales			(0.1)	(0.3)			(0.9)	(0.4)					(1.3)
Operating and maintenance expense			(0.1)	(0.2)			0.4	(0.5)					(1.0)
Depreciation and amortization expense				(0.1)				(0.2)					(0.3)
Taxes other than income taxes				(0.1)			(0.3)	(0.8)					(0.1)
Interest expense													(0.1)
Income (loss) before taxes			(0.2)	(0.3)			0.4	(2.6)					1.3
(Provision) benefit for income taxes			0.1	0.1			(0.2)	1.0					(0.5)
Discontinued operations, net of tax	6.1	0.9	(0.1)	(0.2)			0.2	(1.6)					0.8
Gain on sale at closing							1.0
Earn-out mechanism period						4 years
Period for which transition services are provided						6 months						6 months
Period from the sale of discontinued operations within which cash flows will expire						2 years
Proceeds related to sale						1.6						2.6
Note receivable from the buyer												$ 4.0
Term of note receivable from the buyer												7 years 6 months