COMMITMENTS AND CONTINGENCIES (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	0 Months Ended	1 Months Ended					3 Months Ended
	Mar. 31, 2013 Weston and Pulliam Plants WPS	Apr. 22, 2013 Columbia and Edgewater WPS	Feb. 29, 2012 Pulliam Title V Air Permit WPS	Jun. 30, 2012 Columbia Title V Air Permit WPS	Mar. 31, 2013 WDNR Issued NOV's WPS NOV	Mar. 31, 2013 Mercury emission MW	Mar. 31, 2013 Mercury emission WPS	Mar. 31, 2013 Manufactured Gas Plant Remediation site
Environmental
Beneficial environmental project amount	$ 6.0	$ 1.3
Civil penalty and legal fees	1.2	0.4
EPA Review Period in Days			45 days
Maximum period over which operation permit would be due				6 months
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								53
Number of environmental remediation sites transferred to the EPA Superfund Alternative Sites Program								20
Estimated and accrued future undiscounted investigation and cleanup costs for all sites								639.6
Cash expenditures for environmental remediation not yet recovered in rates								30.0
Regulatory assets recorded for cash and estimated future remediation expenditures, net of insurance recoveries received								669.6
Insurance recoveries received								$ 63.1