REGULATORY ENVIRONMENT (Details) (USD $) In Millions, unless otherwise specified		0 Months Ended							1 Months Ended				3 Months Ended											0 Months Ended	1 Months Ended	16 Months Ended				0 Months Ended
	Mar. 29, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Entity's original request WPS	Dec. 06, 2012 Public Service Commission of Wisconsin (PSCW) 2013 Rates Settlement agreement WPS	Mar. 29, 2013 Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2014 Rates Entity's original request WPS	Dec. 06, 2012 Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2013 Rates Settlement agreement WPS	Dec. 09, 2011 Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2012 Rates Rate order WPS	Mar. 29, 2013 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2014 Rates Entity's original request WPS	Dec. 06, 2012 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2013 Rates Settlement agreement WPS	Dec. 09, 2011 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2012 Rates Rate order WPS	Jan. 31, 2013 Michigan Public Service Commission (MPSC)	Jan. 31, 2013 Michigan Public Service Commission (MPSC) MGU	Jun. 07, 2013 Michigan Public Service Commission (MPSC) Natural gas rate case 2014 Rates Entity's original request MGU	Jun. 28, 2013 Michigan Public Service Commission (MPSC) Retail electric rate case 2014 Rates Entity's original request UPPCO	Sep. 30, 2012 Michigan Public Service Commission (MPSC) Retail electric rate case 2012 Rates Settlement agreement UPPCO	Mar. 30, 2012 Michigan Public Service Commission (MPSC) Retail electric rate case 2012 Rates Settlement agreement UPPCO	Dec. 20, 2011 Michigan Public Service Commission (MPSC) Retail electric rate case 2012 Rates Settlement agreement UPPCO	Jun. 30, 2013 Illinois Commerce Commission (ICC) 2012 Rates NSG	Mar. 31, 2013 Illinois Commerce Commission (ICC) 2012 Rates NSG	Jun. 30, 2013 Illinois Commerce Commission (ICC) 2012 Rates PGL	Mar. 31, 2013 Illinois Commerce Commission (ICC) 2012 Rates PGL	Jun. 18, 2013 Illinois Commerce Commission (ICC) Natural gas rate case 2013 Rates Rate order NSG	Jun. 18, 2013 Illinois Commerce Commission (ICC) Natural gas rate case 2013 Rates Rate order PGL	Jan. 10, 2012 Illinois Commerce Commission (ICC) Natural gas rate case 2012 Rates Rate order NSG	Jan. 10, 2012 Illinois Commerce Commission (ICC) Natural gas rate case 2012 Rates Rate order PGL	Jul. 13, 2012 Minnesota Public Utilities Commission (MPUC) Natural gas rate case 2011 Rates Rate order	May 31, 2010 Federal Energy Regulatory Commission (FERC) Seams Elimination Charge Adjustment (SECA) Integrys Energy Services item	Mar. 31, 2006 Federal Energy Regulatory Commission (FERC) Seams Elimination Charge Adjustment (SECA) Integrys Energy Services	Jul. 31, 2013 Subsequent Event Public Service Commission of Wisconsin (PSCW) 2014 Rates Regulatory authority staff recommendations WPS	Jul. 31, 2013 Subsequent Event Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2014 Rates Regulatory authority staff recommendations WPS	Jul. 31, 2013 Subsequent Event Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2014 Rates Regulatory authority staff recommendations WPS	Jul. 31, 2013 Subsequent Event Federal Energy Regulatory Commission (FERC) Settlement agreement Seams Elimination Charge Adjustment (SECA) Integrys Energy Services
Regulatory Proceedings:
Requested rate increase (decrease)			$ 19.0			$ 71.1					$ 8.0	$ 7.9
Requested return on common equity percent	10.75%										10.75%	10.75%
Requested percent of capital structure composed of common equity	51.11%										50.12%	54.98%
Authorized rate increase (decrease)				(3.4)	(7.2)		28.5	8.1							4.2					6.6	57.2	1.9	57.8	11.0
Estimated fuel refund including carrying costs							20.5
Deferred related to pension and other employee benefit costs				2.1
Authorized return on common equity percent		10.30%													10.20%					9.28%	9.28%	9.45%	9.45%	9.70%
Authorized percent of capital structure composed of common equity		51.61%													54.90%					50.32%	50.43%	50.00%	49.00%	50.48%
Authorized recovery of income tax amounts previously expensed related to the Federal Health Care Reform Act		5.9
Expenses related to electric decoupling														1.5
Reversal of expenses related to electric decoupling													1.5
Expected recovery related to decoupling mechanisms																	1.7		14.8
Recovery related to decoupling mechanisms																0.5		4.6
Annual cap for decoupling				8.0			14.0
Percentage of price variance from the cost of fuel and purchased power included in rates								2.00%
Notification of depreciation study as a result of reversal of rulings									2.5
Reduction to depreciation expense										(2.5)
Trial basis period																								3 years
Transition period when charges paid																										16 months
Billings received																										19.2
Favorable rulings, number of issues																									2
Receivable related to favorable settlement ruled by FERC																									3.8
Settlement agreement amount																														9.5
Annual cap on services															1.50%									10.00%
Recommended rate increase (decrease)																												$ 7.8	$ 9.3
Recommended return on common equity percent																											10.20%
Recommended percent of capital structure composed of common equity																											50.14%
Period from the effective date of agreement within which lump sum payment is to be made																														5 days
Period from the effective date of agreement within which petitions for reviewed filed with U.S. Court of Appeals is to be withdrawn																														5 days