REGULATORY ENVIRONMENT (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	1 Months Ended														3 Months Ended				1 Months Ended						16 Months Ended	1 Months Ended
	Sep. 30, 2012 WPS	Sep. 30, 2012 WPS	Mar. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Entity's original request WPS	Aug. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Regulatory authority staff recommendations WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) 2013 Rates Rate order WPS	Mar. 31, 2013 Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2014 Rates Entity's original request WPS	Aug. 31, 2013 Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2014 Rates Regulatory authority staff recommendations WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2013 Rates Rate order WPS	Dec. 31, 2011 Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2012 Rates Rate order WPS	Mar. 31, 2013 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2014 Rates Entity's original request WPS	Aug. 31, 2013 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2014 Rates Regulatory authority staff recommendations WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2013 Rates Rate order WPS	Dec. 31, 2011 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2012 Rates Rate order WPS	Jan. 31, 2013 Michigan Public Service Commission (MPSC) MGU	Jun. 30, 2013 Michigan Public Service Commission (MPSC) Retail electric rate case 2014 Rates Entity's original request UPPCO	Dec. 31, 2011 Michigan Public Service Commission (MPSC) Retail electric rate case 2012 Rates Rate order UPPCO	Sep. 30, 2012 Michigan Public Service Commission (MPSC) Retail electric rate case 2012 Rates Rate order UPPCO	Mar. 30, 2012 Michigan Public Service Commission (MPSC) Retail electric rate case 2012 Rates Rate order UPPCO	Sep. 30, 2013 Illinois Commerce Commission (ICC) 2012 Rates NSG	Sep. 30, 2013 Illinois Commerce Commission (ICC) 2012 Rates PGL	Jun. 30, 2013 Illinois Commerce Commission (ICC) Natural gas rate case 2013 Rates Rate order NSG	Jun. 30, 2013 Illinois Commerce Commission (ICC) Natural gas rate case 2013 Rates Rate order PGL	Jan. 31, 2012 Illinois Commerce Commission (ICC) Natural gas rate case 2012 Rates Rate order NSG	Jan. 31, 2012 Illinois Commerce Commission (ICC) Natural gas rate case 2012 Rates Rate order PGL	Sep. 30, 2013 Minnesota Public Utilities Commission (MPUC) Natural gas rate case 2014 Rates Entity's original request MERC	Jul. 31, 2012 Minnesota Public Utilities Commission (MPUC) Natural gas rate case 2011 Rates Rate order MERC	Mar. 31, 2006 Federal Energy Regulatory Commission (FERC) Seams Elimination Charge Adjustment (SECA) Integrys Energy Services	Sep. 30, 2013 Federal Energy Regulatory Commission (FERC) Settlement agreement Seams Elimination Charge Adjustment (SECA) Integrys Energy Services	Sep. 30, 2013 Federal Energy Regulatory Commission (FERC) Settlement agreement Seams Elimination Charge Adjustment (SECA) Integrys Energy Services	Oct. 31, 2013 Subsequent Event Public Service Commission of Wisconsin (PSCW) 2014 Rates Entity's revised request WPS	Oct. 31, 2013 Subsequent Event Public Service Commission of Wisconsin (PSCW) Natural gas rate case 2014 Rates Entity's revised request WPS	Oct. 31, 2013 Subsequent Event Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2014 Rates Entity's revised request WPS	Oct. 31, 2013 Subsequent Event Michigan Public Service Commission (MPSC) Natural gas rate case 2014 Rates Settlement agreement MGU
Regulatory Proceedings:
Requested rate increase (decrease)						$ 19.0				$ 71.1					$ 7.9										$ 14.2						$ 14.0	$ 60.0
Requested return on common equity percent			10.75%												10.75%										10.75%					10.60%
Requested recovery for the Wisconsin retail allocation of environmental remediation capital and operating costs related to the Consent Decree																														1.7
Requested percent of capital structure composed of common equity			51.11%												54.98%										50.31%
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												20.5
Deferral 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	5.9			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																			0.8	6.4
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%
Reversal of disallowance of depreciation expense associated with the retirement of certain assets														2.5
Reduction to depreciation expense														(2.5)
Trial basis period for decoupling mechanism																										3 years
Transition period when charges paid																											16 months
Seams elimination charge adjustment (SECA) billings paid																											19.2
Receivable related to favorable settlement ruled by FERC																													3.8
Settlement agreement rate increase (decrease)																																	4.5
Annual percent cap on decoupling based on distribution revenues approved in the rate case																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%
Return on common equity per settlement agreement																																	10.25%
Percent of capital structure composed of equity per settlement agreement																																	48.62%
Lump sum payment received																												9.5
Additional income recognized as a result of a settlement agreement																													5.7
Amount awarded as part of a settlement agreement																													$ 9.5