COMMITMENTS AND CONTINGENCIES (Details 2) (USD $) In Millions, unless otherwise specified		1 Months Ended				12 Months Ended
	Dec. 31, 2011 EPA settlements with other utilities	Dec. 31, 2011 WDNR Issued NOV's Violation	Oct. 31, 2010 Pulliam Title V Air Permit d	Jul. 31, 2010 Columbia Title V Air Permit d	Dec. 31, 2011 Mercury emission MW	Dec. 31, 2005 Sulfur dioxide and nitrogen oxide emissions State	Dec. 31, 2011 Manufactured gas plant remediation site
Environmental remediation obligations
Fines, penalties, and costs of supplemental environmental projects associated with settlements, low end of range	$ 6
Fines, penalties, and costs of supplemental environmental projects associated with settlements, high end of range	30
Number of NOV's alleging violations of the air permits received since 2008		4
Number of NOV's for clerical error received since 2008		1
Number of corrective actions taken for NOV's received		5
Number NOV's dismissed		2
Number of NOV's referred to the state Justice Department		3
Number of days which the EPA directed WDNR to resolve renewal objection				90
Number of days which the EPA reviewed proposed permit			45
Environmental remediation obligations
Percentage mercury reduction from 2002 through 2004 baseline, required by Best Available Control Technology rule in Phase I					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 beginning year 2015, required by Best Available Control Technology rule in Phase II					90.00%
Level of electric generating units above which a reduction in mercury emissions is required by 2015 (in MW)					25
Estimated capital cost to achieve required emission reduction					2
Number of states included in the CAIR regulation						29
Environmental remediation obligations
Number of environmental remediation sites							54
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							613.7
Regulatory assets recorded for cash and estimated future remediation expenditures, net of insurance recoveries received							625.9
Insurance recoveries received							59.9
Cash expenditures for environmental remediation not yet recovered in rates							$ 12.2