COMMITMENTS AND CONTINGENCIES (Details 2) (USD $) In Millions, unless otherwise specified	6 Months Ended	1 Months Ended		1 Months Ended					12 Months Ended	6 Months Ended
	Jun. 30, 2012 Weston and Pulliam Plants item	Dec. 31, 2011 WDNR Issued NOV's nov	Jun. 30, 2012 WDNR Issued NOV's nov	Oct. 31, 2010 Pulliam Title V Air Permit D	Jun. 30, 2012 Columbia Title V Air Permit D	Jun. 30, 2012 Mercury emission	Jun. 30, 2012 Mercury emission Phase I	Jun. 30, 2012 Mercury emission Phase II megawatt	Dec. 31, 2005 Sulfur Dioxide and Nitrogen Oxide Emissions state	Jun. 30, 2012 Manufactured Gas Plant Remediation site
Environmental
Number of remedial steps required, minimum	1
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 for enforcement		3
E P A Review Period in Days				45
Number of days which the EPA directed WDNR to resolve renewal objection					90
Period within which notice is due if operation permit is required to be submitted					6 months
Environmental
Percentage mercury reduction required by Best Available Control Technology 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 Best Available Control Technology rule								90.00%
Level of electric generating units above which a reduction in mercury emissions (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										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										70.8
Regulatory assets recorded for cash and estimated future remediation expenditures, net of insurance recoveries received										79.4
Insurance recoveries received										$ 22.3