SHORT-TERM BORROWINGS AND SHORT-TERM BANK LINES OF CREDIT (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010
Line of Credit Facility [Line Items]
Amount of outstanding cash borrowings	$ 28.0	$ 9.5
Amount of outstanding commercial paper borrowings	10.5	263.5
Kansas City Power and Light Company [Member]
Line of Credit Facility [Line Items]
Amount of revolving credit facility	600.0
Revolving credit facility expiration date	August 2013
Covenant term - amount considered as default	50.0
Amount of outstanding cash borrowings	0	0
Amount of outstanding commercial paper borrowings	10.5	263.5
Weighted average interest rate from outstanding borrowings	0.35%	0.41%
Line of Credit Facility, Covenant Compliance	in compliance
Amount of letters of credit outstanding	31.5	24.4
Covenant Term Ratio Of Consolidated Indebtedness To Consolidated Capitalization Ratio, Maximum	0.65
KCPL Greater Missouri Operations Company [Member]
Line of Credit Facility [Line Items]
Amount of revolving credit facility	450.0
Revolving credit facility expiration date	August 2013
Covenant term - amount considered as default	50.0
Amount of outstanding cash borrowings	0	0
Line of Credit Facility, Covenant Compliance	in compliance
Amount of letters of credit outstanding	13.2	13.2
Covenant Term Ratio Of Consolidated Indebtedness To Consolidated Capitalization Ratio, Maximum	0.65
Line of credit facility with group of banks [Member]
Line of Credit Facility [Line Items]
Amount of revolving credit facility	200.0
Revolving credit facility expiration date	August 2013
Covenant term - amount considered as default	50.0
Weighted average interest rate from outstanding borrowings	3.00%	3.06%
Line of Credit Facility, Covenant Compliance	in compliance
Amount of letters of credit outstanding	$ 11.6	$ 15.8
Covenant Term Ratio Of Consolidated Indebtedness To Consolidated Capitalization Ratio, Maximum	0.65