REGULATORY ENVIRONMENT (Details) (Public Service Commission of Wisconsin (PSCW), Rate order, USD $) In Millions, unless otherwise specified	1 Months Ended
	Dec. 31, 2013 2014 Rates	Dec. 31, 2013 2014 Rates Retail electric rate case	Dec. 31, 2013 2014 Rates Retail natural gas rate case	Dec. 31, 2012 2013 Rates	Dec. 31, 2012 2013 Rates Retail electric rate case	Dec. 31, 2012 2013 Rates Retail natural gas rate case	Dec. 31, 2011 2012 Rates Retail electric rate case	Dec. 31, 2011 2012 Rates Retail natural gas rate case
Regulatory Proceedings:
Annual increase (decrease) in rates for customers		$ (12.8)	$ 4.0		$ 28.5	$ (3.4)	$ 8.1	$ (7.2)
Return on common equity percent reflected in rates of customers	10.20%			10.30%
Percent of capital structure composed of common equity	50.14%			51.61%
Estimated fuel refund					20.5
Deferral related to pension and other employee benefit 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
Percentage variance from the cost of fuel and purchased power included in rates							2.00%