REGULATORY ENVIRONMENT (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended	1 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Mar. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Entity's original request	Aug. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Regulatory authorities staff recommendations	Mar. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Retail electric rate case Entity's original request	Aug. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Retail electric rate case Regulatory authorities staff recommendations	Mar. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Natural gas rate case Entity's original request	Aug. 31, 2013 Public Service Commission of Wisconsin (PSCW) 2014 Rates Natural gas rate case Regulatory authorities staff recommendations	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) 2013 Rates Rate order	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) 2013 Rates Retail electric rate case Rate order	Dec. 31, 2012 Public Service Commission of Wisconsin (PSCW) 2013 Rates Natural gas rate case Rate order	Dec. 31, 2011 Public Service Commission of Wisconsin (PSCW) 2012 Rates Retail electric rate case Rate order	Dec. 31, 2011 Public Service Commission of Wisconsin (PSCW) 2012 Rates Natural gas rate case Rate order	Oct. 31, 2013 Subsequent Event [Member] Public Service Commission of Wisconsin (PSCW) 2014 Rates Entity's revised request	Oct. 31, 2013 Subsequent Event [Member] Public Service Commission of Wisconsin (PSCW) 2014 Rates Retail electric rate case Entity's revised request	Oct. 31, 2013 Subsequent Event [Member] Public Service Commission of Wisconsin (PSCW) 2014 Rates Natural gas rate case Entity's revised request
Regulatory Proceedings:
Requested rate increase (decrease)					$ 71.1		$ 19.0								$ 60.0	$ 14.0
Recommended percent of capital structure composed of common equity				50.14%
Recommended rate increase (decrease)						9.3		7.8
Requested return on common equity percent			10.75%											10.60%
Recommended return on common equity percent				10.20%
Requested percent of capital structure composed of common equity			51.11%
Authorized rate increase (decrease)										28.5	(3.4)	8.1	(7.2)
Deferral of pension and other employee benefit costs											2.1
Estimated fuel refund										20.5
Authorized return on common equity percent									10.30%
Authorized percent of capital structure composed of common equity									51.61%
Annual cap for decoupling										14.0	8.0
Authorized recovery of income tax amounts previously expensed related to the Federal Health Care Reform Act	5.9	5.9							5.9
Percentage of price variance from the cost of fuel and purchased power included in rates												2.00%
Requested recovery for the environmental remediation costs related to the Consent Decree														$ 1.7