DISPOSITIONS - DISCONTINUED OPERATIONS (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			1 Months Ended	10 Months Ended	1 Months Ended		3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Nov. 30, 2014	Oct. 31, 2014	Sep. 30, 2014	Mar. 31, 2013	Sep. 30, 2012	Nov. 01, 2014
Disclosures related to discontinued operations
Discontinued operations, net of tax	$ 1.8	$ 87.3	$ 45.4
Pre-tax gain (loss) on sale	(24.3)	0	0
Assets and liabilities classified as held for sale on balance sheets
Total assets	0.7	277.9
Total liabilities	0	49.1
Components of discontinued operations recorded in income statements
Provision for income taxes	(7.2)	(45.9)	(22.6)
Discontinued operations, net of tax	1.8	87.3	45.4
IES | IES's retail energy business
Disclosures related to discontinued operations
Discontinued operations, net of tax		82.5	55.1		0.4
Cash proceeds from sale				333.0
Pre-tax gain (loss) on sale		0	0		(28.8)
After-tax gain (loss) on sale					17.3
Transaction costs related to a sale					(4.5)
Maximum number of months after sale that guarantees will be held				6 months
Transition period for services				15 months
Assets and liabilities classified as held for sale on balance sheets
Cash and cash equivalents		5.5							7.6
Accounts receivable and accrued unbilled revenues, net of reserves		390.9							293.8
Accounts receivable and accrued unbilled revenues, reserves		1.7							1.8
Inventories		34.2							52.4
Current assets from risk management activities		229.5							234.8
Prepaid taxes		2.5							0
Other current assets		41.5							75.1
Property, plant, and equipment, net of accumulated depreciation		5.2							4.5
Accumulated depreciation		15.6							16.6
Long-term assets from risk management activities		73.4							106.9
Goodwill		6.7							0
Other long-term assets		26.0							25.5
Total assets		815.4							800.6
Accounts payable		202.9							186.9
Current liabilities from risk management activities		160.6							169.7
Accrued taxes		2.0							0.2
Other current liabilities		13.1							6.7
Long-term liabilities from risk management activities		61.9							79.5
Other long-term liabilities		7.0							0.3
Total liabilities		447.5							443.3
Components of discontinued operations recorded in income statements
Revenues		2,150.9	1,201.0		2,587.1
Cost of sales		(1,910.7)	(1,018.9)		(2,444.7)
Operating and maintenance expense		(105.6)	(88.3)		(91.5)
Depreciation and amortization expense		(3.2)	(3.4)		(2.7)
Taxes other than income taxes		(3.2)	(2.4)		(4.9)
Goodwill impairment loss		0	0		(6.7)
Miscellaneous income		7.9	0.3		0.6
Interest expense		(0.8)	(1.3)		(0.7)
Income (loss) before taxes		135.3	87.0		7.7
Provision for income taxes		(52.8)	(31.9)		(7.3)
Discontinued operations, net of tax		82.5	55.1		0.4
Holding Company and Other | Combined Locks Energy Center
Disclosures related to discontinued operations
Discontinued operations, net of tax	(0.5)	(1.3)	(0.6)
Assets and liabilities classified as held for sale on balance sheets
Total assets	0.7	0.7
Components of discontinued operations recorded in income statements
Discontinued operations, net of tax	(0.5)	(1.3)	(0.6)
Holding Company and Other | Uncertain tax positions
Disclosures related to discontinued operations
Discontinued operations, net of tax	0.7	5.9	1.8
Components of discontinued operations recorded in income statements
Discontinued operations, net of tax	0.7	5.9	1.8
Holding Company and Other | WPS Empire State, Inc | WPS Beaver Falls Generation, LLC and WPS Syracuse Generation, LLC
Disclosures related to discontinued operations
Discontinued operations, net of tax	1.2	0.2	(4.0)
Pre-tax gain (loss) on sale	1.0
Pre-tax impairment loss			1.1
After-tax impairment loss			0.7
Earn-out mechanism period							4 years
Earn-out settlement payment						2.0
Components of discontinued operations recorded in income statements
Revenues	0	1.2	0.6
Cost of sales	0	(0.9)	(2.0)
Operating and maintenance expense	2.0	0.4	(3.5)
Depreciation and amortization expense	0	0	(0.6)
Taxes other than income taxes	0	(0.3)	(1.4)
Miscellaneous income	0	0	0.3
Income (loss) before taxes	2.0	0.4	(6.6)
Provision for income taxes	(0.8)	(0.2)	2.6
Discontinued operations, net of tax	1.2	0.2	(4.0)
Holding Company and Other | Sunbury Holdings, LLC | WPS Westwood Generation, LLC
Disclosures related to discontinued operations
Discontinued operations, net of tax			(6.9)
Pre-tax gain (loss) on sale		(0.6)
Pre-tax impairment loss								8.4
After-tax impairment loss								5.0
Components of discontinued operations recorded in income statements
Revenues			9.2
Cost of sales			(4.4)
Operating and maintenance expense			(14.3)
Depreciation and amortization expense			(1.0)
Taxes other than income taxes			(0.2)
Interest expense			(0.7)
Income (loss) before taxes			(11.4)
Provision for income taxes			4.5
Discontinued operations, net of tax			$ (6.9)