COMMITMENTS AND CONTINGENCIES (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	1 Months Ended			6 Months Ended
	Mar. 31, 2013 Weston and Pulliam Plants	Jun. 30, 2013 Columbia And Edgewater	Jun. 30, 2013 WDNR Issued NOV's NOV	Jun. 30, 2013 Mercury emission MW	Jun. 30, 2013 Manufactured Gas Plant Remediation site
Environmental
Beneficial environmental project amount	$ 6.0	$ 1.3
Civil penalty	1.2
Civil penalty and legal fees		0.4
Environmental
Number of NOV's alleging violations of the air permits received since 2008			4
Number of corrective actions taken for NOV's received			5
Environmental
Percentage mercury reduction required by the State of Wisconsin's mercury rule				40.00%
Level of electric generating units above which a 90% reduction in mercury emissions is required by 2015 (in MW)				150
Percentage mercury reduction required by the State of Wisconsin's mercury rule, for electric generating units above 150 MW				90.00%
Level of electric generating units above which a reduction in mercury emissions is required (in MW)				25
Estimated capital cost to achieve required emission reduction				8
Environmental remediation obligations
Number of environmental remediation sites					10
Number of environmental remediation sites transferred to the EPA Superfund Alternative Sites Program					7
Estimated and accrued future undiscounted investigation and cleanup costs for all sites					65.5
Cash expenditures for environmental remediation not yet recovered in rates					14.1
Regulatory assets recorded for cash and estimated future remediation expenditures, net of insurance recoveries received					79.6
Insurance recoveries received					$ 24.7