REGULATORY ENVIRONMENT (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended													3 Months Ended	1 Months Ended								9 Months Ended	1 Months Ended
	Aug. 31, 2014 Public Service Commission of Wisconsin (PSCW) 2015 Rates WPS	Apr. 30, 2014 Public Service Commission of Wisconsin (PSCW) 2015 Rates WPS	Dec. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) 2013 Rates WPS	Aug. 31, 2014 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2015 Rates WPS	Apr. 30, 2014 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2015 Rates WPS	Dec. 31, 2013 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2014 Rates WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2013 Rates WPS	Aug. 31, 2014 Public Service Commission of Wisconsin (PSCW) Retail natural gas rate case 2015 Rates WPS	Apr. 30, 2014 Public Service Commission of Wisconsin (PSCW) Retail natural gas rate case 2015 Rates WPS	Dec. 31, 2013 Public Service Commission of Wisconsin (PSCW) Retail natural gas rate case 2014 Rates WPS	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) Retail natural gas rate case 2013 Rates WPS	Jan. 31, 2013 Michigan Public Service Commission (MPSC) MGU	Mar. 31, 2013 Michigan Public Service Commission (MPSC) MGU	Dec. 31, 2013 Michigan Public Service Commission (MPSC) Retail electric rate case 2014 Rates UPPCO	Nov. 30, 2013 Michigan Public Service Commission (MPSC) Retail natural gas rate case 2014 Rates MGU	Feb. 28, 2014 Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates NSG	Feb. 28, 2014 Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates PGL	Dec. 31, 2013 Illinois Commerce Commission (ICC) Retail natural gas rate case 2013 Rates NSG	Jun. 30, 2013 Illinois Commerce Commission (ICC) Retail natural gas rate case 2013 Rates NSG	Dec. 31, 2013 Illinois Commerce Commission (ICC) Retail natural gas rate case 2013 Rates PGL	Jun. 30, 2013 Illinois Commerce Commission (ICC) Retail natural gas rate case 2013 Rates PGL	Sep. 30, 2014 Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2014 Rates MERC	Jul. 31, 2012 Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2011 Rates MERC	Oct. 31, 2014 Subsequent Event Retail natural gas rate case 2015 Rates NSG	Oct. 31, 2014 Subsequent Event Retail natural gas rate case 2015 Rates PGL	Oct. 31, 2014 Subsequent Event Public Service Commission of Wisconsin (PSCW) 2015 Rates WPS	Oct. 31, 2014 Subsequent Event Public Service Commission of Wisconsin (PSCW) Retail electric rate case 2015 Rates WPS	Oct. 31, 2014 Subsequent Event Public Service Commission of Wisconsin (PSCW) Retail natural gas rate case 2015 Rates WPS	Oct. 31, 2014 Subsequent Event Michigan Public Service Commission (MPSC) Retail electric rate case 2015 Rates WPS	Oct. 31, 2014 Subsequent Event Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates NSG	Oct. 31, 2014 Subsequent Event Illinois Commerce Commission (ICC) Retail natural gas rate case 2015 Rates PGL	Oct. 31, 2014 Subsequent Event Minnesota Public Utilities Commission (MPUC) Retail natural gas rate case 2014 Rates MERC
Regulatory Environment
Requested annual increase (decrease) in rates for customers						$ 76.8				$ (1.6)							$ 7.1	$ 128.9												$ 5.7
Requested return on common equity percent		10.60%																												10.60%
Requested percent of capital structure composed of common equity		50.51%															50.41%	50.31%												50.48%
Recommended rate increase (decrease) in rates for customers					28.7				(13.6)																(1.0)	45.5					3.5	71.1
Recommended rate of return on common equity	10.20%																								9.15%	9.15%					9.00%	9.00%
Recommended percent of capital structure composed of common equity	50.27%																														50.48%	50.33%
Revised requested annual increase (decrease) in rates for customers																												48.0	(8.0)		6.5	100.5
Revised requested return on common equity percent																	10.25%	10.25%									10.20%				10.25%
Revised requested percent of capital structure composed of common equity																											50.27%				50.48%	50.33%
Approved annual increase (decrease) in rates for customers							(12.8)	28.5			4.0	(3.4)			5.8	4.5				6.6		57.2		11.0									7.6
Approved return on common equity percent reflected in rates of customers			10.20%	10.30%											10.15%	10.25%				9.28%		9.28%		9.70%									9.35%
Approved percent of capital structure composed of common equity			50.14%	51.61%											56.74%	48.62%				50.32%		50.43%		50.48%									50.31%
Fuel refund								20.5
Deferral related to pension and other employee benefits costs								7.3				2.1
Recovery of income tax amounts previously expensed related to the Federal Health Care Reform Act				5.9
Annual cap for decoupling								14.0				8.0
Reversal of disallowance of depreciation expense associated with the retirement of certain assets													2.5
Reduction to depreciation expense														(2.5)
Adjustment to annual increase (decrease) in rates for customers																			0.1		2.6
Interim rates to be refunded to customers																							$ 2.3
Trial basis period for decoupling mechanism																								3 years
Annual percent cap on decoupling based on distribution revenues approved in the rate case																								10.00%									0.00%