COMMITMENTS AND CONTINGENCIES (Details 2) (USD $) In Millions, unless otherwise specified		1 Months Ended	12 Months Ended							12 Months Ended								1 Months Ended	12 Months Ended		1 Months Ended
	Dec. 31, 2009 MW	Jun. 30, 2006 Gas site	Dec. 31, 2011 Gas	Dec. 31, 2011 Permits Electric Y	Dec. 31, 2011 SO2 Emissions Electric T	Dec. 31, 2011 Clean Air Interstate Rule Electric state MW	Dec. 31, 2011 NAAQS Electric ppb Y	Jan. 06, 2010 NAAQS Electric Minimum ppb	Jan. 06, 2010 NAAQS Electric Maximum ppb	Dec. 31, 2011 Power Plant Mercury And Air Toxics Rule Y	Dec. 31, 2011 Power Plant Mercury And Air Toxics Rule Electric phase	Dec. 31, 2011 Power Plant Mercury And Air Toxics Rule Electric Minimum	Dec. 31, 2011 Power Plant Mercury And Air Toxics Rule Electric Maximum	Dec. 31, 2011 Surface Impoundments Electric option	Dec. 31, 2011 Surface Impoundments Iatan Electric	Dec. 31, 2011 Surface Impoundments Plum point Electric	Sep. 22, 2009 Green House Gases Electric T	Nov. 30, 2010 Renewable Energy Electric	Dec. 31, 2011 Renewable Energy Electric certificate mWh	Nov. 04, 2008 Renewable Energy Electric customer	Mar. 31, 2011 National Emission Standards for Hazardous Air Pollutants Electric Y
Environmental Laws And Regulations
Number of years site operating permits are valid				5
Expected cost of adding Carbon injection system												$ 112	$ 130
Period for compliance (in years)										3											4
Amount of total power capacity of generating facility (in megawatts)	18
Amount of SO2 emission permitted under each SO2 allowance per affected unit (in tons)					1
Minimum capacity of power plant called to reduce emission levels of SO2 and NOx (in megawatts)						25
Number of states in which fossil-fueled power plants are required to reduce emission levels of SO2 and NOx as per CAIR						28
Ratio of S02 allowances that must be utilized						2:1
Percentage of SO2 reduction from 2005 levels by 2014, required by the proposed CATR						73.00%
Percentage of NOx reduction from 2005 levels by 2014, required by the proposed CATR (as a percent)						54.00%
Proposed primary standard								60	70
Normal reconsideration period for ozone standards (in years)							5
2008 standard at which states will continue to identify and designate all non-attainment areas							75
Phase-in period for proposed standards (in years)																					3
Number of phases expected to reduce nationwide mercury emissions											2
Minimum emission threshold of CO2e from power generating and certain other facilities requires to report Greenhouse Gases (in metric tons)																	25,000
Percentage of ownership in a coal ash impoundment at a generating facility															12.00%	7.52%
Number of options in the EPA proposal														2
Potential cost for construction of new landfill and conversion of existing ash handling from wet to dry system(s)														15
Minimum percentage of energy purchased through long-term Purchased Power Agreements																			15.00%
Amount of renewable energy certificates generated each year																			900,000
Represents the megawatt-hour of renewable energy per renewable energy certificate (REC)																			1
Minimum percentage of Missouri retail sales required to generate or purchase electricity by 2011																			2.00%	2.00%
Minimum percentage of Missouri retail sales required to generate or purchase electricity by 2021																			15.00%	15.00%
Number of customers who have challenged exemption from solar requirement																				2
Percentage of Missouri retail sales required to generate or purchase solar energy																				2.00%
Percentage of Kansas retail customer peak capacity required to be sourced from renewable energy by 2011																		10.00%
Percentage of Kansas retail customer peak capacity required to be sourced from renewable energy by 2016																		15.00%
Percentage of Kansas retail customer peak capacity required to be sourced from renewable energy by 2020																		20.00%
Number of former manufactured plant sites with potential future remediation		2
Remediation costs			$ 0.2